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Mendelian Genetics — Transcript

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0:00hi everybody
0:03in this lecture
0:05i would like to speak with you
0:08about
0:09mendelian
0:10genetics
0:15since the beginning of human history
0:18people have wondered how traits are
0:22inherited from one generation to the
0:25next
0:28kids
0:29look like their parents
0:31and their siblings
0:35and
0:36we were able to develop
0:38a lot of domestic plants
0:41and animals
0:43which are bred for useful traits by
0:47controlled matings
0:52it's all about
0:54inheritance
0:58the study of inheritance
1:01has two sides to the same coin
1:06inheritance is about
1:09similar phenotype
1:12but also
1:13about
1:15variation
1:17a union between a male and a female
1:21is well over
1:2464 trillion
1:26genetic combination
1:30that's
1:32a big house if you want to
1:35understand the rules of genetics
1:39with such a huge
1:40variation
1:43however
1:44the field of modern genetics
1:49gave us the tools to understand
1:52inheritance rules
1:55there are rules that control inheritance
1:59and
2:00this lecture
2:02is going to simplify
2:04some of them for you
2:09so what are the goals that control
2:12inheritance
2:15one possible explanation of readity
2:19is the blending hypothesis
2:24the idea that genetic material
2:27contributed by two parents
2:31is mixed
2:32in a manner analog to the way that blue
2:36and yellow paints can make green
2:40that's one direction
2:42that
2:43you can take
2:46intuitively
2:47blending hypotheses makes sense in
2:51a daily life
2:54i will take my cat as an example
2:59all i know about is heritage
3:02is that it was born on the streets of
3:06the city of toronto
3:09i do not know anything
3:12about its genetic background
3:16now if you cross such a cat
3:21with another
3:23cat
3:24with unknown genetic background
3:28you will get a mixed phenotype
3:32something like that well maybe
3:35but
3:36you're going to have some phenotype from
3:39this cat
3:41and some phenotype from the other cat
3:47so
3:49the overall phenotype
3:52will be something in between
3:58an alternative to the blending model
4:02is the
4:03particulate hypothesis of inheritance
4:09the gene ideal
4:13pass a discrete
4:16heretable
4:18units
4:19genes
4:20to their kids
4:23for example
4:24here
4:26you have two options
4:28of color
4:30purple
4:32and
4:33white
4:36the f1 generation
4:38that came from a crossing between those
4:42two plants
4:44the hybrid in between the two
4:47is not going to have a light purple
4:52as compared to the parent
4:54it's going to have exactly
4:57the same color
4:59as one of the parent
5:01one way
5:03or
5:04the other
5:08up until the end of the 19th century
5:13if you would run a poll
5:1599.9
5:17of the people
5:19would say that the blending theory
5:23fit best with the rules of inheritance
5:28that's what you can see in nature
5:31people
5:32and in most of the farm animals and
5:34plants
5:39gregor mendel
5:41challenged the existing general
5:44understanding
5:46of genetics at the time
5:51his work when the pea plants which we
5:54used as a model
5:57made him to discover
5:59the fundamental
6:01laws of inheritance
6:07let's start
6:09with some definitions
6:11that will help us to understand
6:14mendelian genetics
6:18a trait
6:19is any characteristics
6:22of an individual
6:28each
6:29visible
6:30trait
6:31is called
6:33phenotype
6:38heredity
6:40is the transmission of traits
6:44from parents
6:46to their offspring
6:50hereditary determinants for traits
6:54are called
6:56genes
7:00alleles
7:01of different versions of a gene
7:08the combination of alleles in the
7:12individual
7:14is called its genotype
7:20individuals with two copies of the same
7:23allele
7:25how
7:26homozygotes
7:30and those with different copays of the
7:34same allele
7:36are
7:37heterozygotes
7:42an organism that is homozygote for a
7:45particular gene
7:47have a pair of identical
7:50alleles
7:52for that gene
7:55an organism that is heterozygous
7:58for a particular gene
8:02as a pair of alleles that are different
8:07for that gene
8:11gregor mendel
8:14during the middle of the
8:1619th century gregor mendel
8:20an austrian monk
8:22and plant scientist
8:26study
8:28the
8:28principles
8:30of hereditary
8:35many think that
8:37mendel was a full-time monk
8:42and was doing the scientific work on the
8:45side
8:47as an hobby
8:49however
8:50that was not the case
8:55during the middle of the
8:5719th century
9:00it became apparent to the policy maker
9:05in the center of europe
9:08that they must find a way
9:11to improve crops and animals
9:16the spanish or portuguese at that time
9:19[Music]
9:20both new animals and plants to europe
9:25from the new world
9:28and the
9:30austro-hungarian empire felt they are
9:33going to lose their superiority
9:37that they add up to this stage
9:42they recruited
9:44young people
9:45to monasteries
9:48which were operating as
9:51biotech
9:52high-tech
9:54the head of the program in bruno
9:59realized that one young person gregor
10:03mendel
10:05was not like
10:06most of the others
10:10first it came from a poor
10:13family all the others came from rich
10:18families
10:19but grego mendel
10:21was the son
10:23of a peasant farmer
10:27and
10:28in such poor families
10:31you cannot be
10:33spoiled so much
10:36you need to
10:37work hard
10:39for your goals
10:42no shortcuts
10:44gregor mendel was working
10:47differently
10:50it was very slow in his progress
10:54and for several years it did something
10:58that the others thought it is not
11:01important
11:03he was working
11:06on setting up his
11:08experimental
11:11system
11:14that's a very
11:16important
11:18and time-consuming stage of research
11:23when i
11:24did my phd work
11:27well i spent over two years
11:31just to set up my system
11:35just to develop the methods how to study
11:39the scientific problem
11:43so mendel went to the market
11:48and he got the
11:50different kinds of peace
11:55his first question he asked himself is
12:00well if i study inheritance
12:04i have to start with something
12:07with the constant property
12:11well it was not obvious at the time that
12:14the most important things to do
12:17if you want to study inheritance is not
12:21to start with courses
12:24but to set up your experimental
12:28system
12:29to make sure
12:31it is working
12:32works on it
12:34constantly
12:36and the same way and when you're doing
12:38the same
12:39experiments twice you're getting exactly
12:43the same
12:44result
12:47mendel devoted ears
12:50to create the reagent for his experiment
12:54and those reagents were mainly
12:58through breeding peace
13:00which are homozygote
13:03for certain traits
13:06so for each of the trait he made sure
13:10that
13:11if he crossed them
13:13to themselves
13:16the same property
13:18and only the same property
13:22would be
13:23observed
13:26either
13:28or
13:29a situation
13:32in which there is a choice between
13:35two different
13:37options
13:39but both together
13:41are not
13:43possible
13:46so gregor mendel
13:48made sure
13:50that
13:51he started his experiment with varieties
13:57that are true breeding homozygotes
14:02mendel tracked only those characters
14:06that vary in an either or manner
14:10one way
14:12or another
14:17and
14:19there is an other things that mendel did
14:22first
14:24he made the choice
14:26of the model that he want to use
14:32and here
14:34he decided to work
14:37on pea plants
14:40first
14:41because they are easy to grow in a small
14:45garden
14:47this is the garden
14:49that he was using
14:52very small
14:54well i mean if you want to work with
14:57goats
14:58cows
15:00that's not going to
15:02help you
15:03a lot
15:06so that's the gowden
15:08that he was using
15:11are two old pictures
15:13that probably are coming more or less
15:16from the time of mandel or maybe a bit
15:19afterwards
15:20and this is a
15:23photo from 1996.
15:27so
15:28making the choice
15:30of the model
15:32was based on the resources that he had
15:37around him
15:39that's a clever decision
15:41to make a model
15:43that you can manage
15:47we learned a lot from mendel's approach
15:51we learned that to make a model that you
15:55can manage you need to study
15:58organisms that are easy to find
16:03many organisms that we are using as a
16:06model well i mean there's an organism
16:08that you can find in the kitchen
16:11yeast
16:13that we can use for making bread
16:16is a very important
16:19model
16:20for many things including cancer
16:24fruit fly
16:25that grow well on rotten vegetable
16:29well i mean that's an excellent animal
16:31model
16:33to study genetics
16:36it was initiated by thomas hunt morgan
16:40he was the first one to use the fruit
16:43fly but
16:44that was a good idea to use an animal
16:49that you have it anywhere in your
16:51kitchen
16:52if you have some rotten tomatoes or
16:55potatoes or other type of vegetables
17:00mold that you can find on old bread
17:04were used also
17:06as a model
17:09mendel
17:10made plans to
17:13reduce
17:14environmental effect on
17:17his
17:18experiments the garden
17:22was in the corner
17:24of two wings of the building
17:28and it was quite protected from wind
17:31that can move poland from one planet to
17:35another
17:36he wanted to control
17:39the
17:40pollination
17:42of plants
17:45and using
17:47the location over here
17:50was quite important
17:57and there is another factor
18:00peas are coming in many varieties
18:05a lot of traits to choose from
18:09mendel started with approximately
18:1234 traits
18:15but later he decided to concentrate on
18:20seven
18:21traits
18:26there are many resources
18:29about genetics that you can find
18:32in this
18:34website
18:35dna from the beginning
18:39and here you're going to see few
18:42animations which i picked up them
18:45from
18:46this website
18:51so
18:53let's go
18:55to mendel's experiment
19:00so this is gregor mendel
19:03he was working on pea plants
19:06because they are easy to grow
19:09they have many threads that distinguish
19:11strands of peace
19:13from each other
19:17and
19:18what he actually did
19:21in order
19:22to look for crosses in between peas with
19:27different traits
19:30is
19:31the following
19:33what you see here
19:35is a mature flower
19:40inside
19:41you can see the stamen
19:44which is the male sex part
19:47the stamen mature first and drop pollens
19:52inside the immature flower
19:57later on
19:58the pistol which is the female sex part
20:02matured and its eggs can be fertilized
20:07by the pond
20:09that land on the pestle
20:12so
20:12that's the way
20:14that most plants are being fertilized
20:18myself self-pollination
20:22the
20:23pistol
20:24and the stamens
20:26are formed the same
20:28flower
20:32but the mendel
20:34decided to control those courses
20:37by
20:38making sure
20:40that the pawns are coming
20:44from another plan that it shows
20:48so what he did
20:50in order to have cross
20:53fertilization
20:54of his pea plants
20:59he
21:00cut
21:01their stamens
21:04before they mature
21:06and
21:07dropped pollens
21:12and now
21:14it was in the position
21:17to take poland from other plants
21:22and to use them
21:24for
21:25the
21:26cross
21:27fertilization
21:28experiment
21:30that it did
21:34so in nature
21:35that would
21:37be
21:37outdoing
21:39they're picking up poland from one plant
21:42and moving it to another plant
21:47oh
21:48in many other cases
21:50the
21:51flowers are
21:54self
21:55fertilized
21:57but in those cases of course
21:59fertilization in nature
22:02is done by insects in most of the cases
22:06so by keeping track of the progeny from
22:12self fertilization and cross
22:14fertilization events
22:16regular mendel to study
22:19how
22:20pea plants traits are inherited
22:25pea plants have quite a lot of
22:28distinctive threats
22:32and
22:33he decided to work with seven
22:37of them
22:40let's go
22:42to his experiments
22:45with seed color
22:49so
22:51as i mentioned earlier
22:53regula mendel
22:55created purebred strains
22:59that when you
23:00self fertilize them
23:03you're going to see always
23:06the same trait
23:10so one of them was yellow when you
23:12self-fertilized yellow
23:15you are going to have only yellow
23:17phenotype when you self fertilize green
23:21plants you're always going to have
23:24green plants
23:26as their progenies
23:30so
23:31we start with a pure bread
23:35what he found
23:38is that when you cross between yellow
23:41and green
23:42you're not going to have
23:44yellow green progeny
23:48when it was crossing yellow and green
23:52all the progenies
23:54were
23:55really yellow
23:57like
23:58the yellow parent
24:01it was not something
24:04in between
24:07so it's not blending
24:10and that's what he had in all the other
24:12traits
24:14one way
24:16or another
24:19it was never
24:21something in between
24:24it was exactly
24:27like one
24:29parent
24:37so
24:38in crossing between
24:40the
24:41yellow p and the green p
24:45oh
24:46the
24:48f1
24:50the progenies
24:52were yellow
24:54like the parent
24:58but when you take
25:02the f1 the progenies and you are making
25:06between them or you are doing
25:08self-fertilization and that's what he
25:10did
25:13i'm going to see something really really
25:15interesting
25:17green
25:19is back
25:22some of the
25:24second generations the f2 which of the
25:27progenies of f1
25:31are green
25:34i mean it wasn't half green it wasn't
25:37yellow green
25:39it was green like their grandparents
25:43was
25:44really green color
25:47the green color
25:49reappear
25:52how we can explain this
25:56we can explain this
25:59in the
26:00following way
26:04the parents generation
26:08was homozygous they had two
26:12yellow
26:13alleles
26:15all dead two green onions
26:19a purebred
26:20green
26:22seeds plant f to green alleles and pure
26:26red yellow
26:28sage plant f to yellow alleles
26:32when
26:34you have fertilization
26:38only
26:38one allele from each p
26:41is involved
26:45so
26:46you're going to have
26:50always heterozygotes in this situation
26:55one allele
26:57is yellow
26:59the other layer
27:02is the green allele
27:10and the phenotype
27:12of detrozygot
27:14is
27:16based on the yellow a lil only
27:21so
27:22since all that zygote offsprings are
27:25yellow
27:26the yellow allele
27:28must be dominant
27:31over
27:32the
27:32recessive green allele
27:36now the green allele did not disappear
27:41its effect
27:43cannot be seen
27:45in the
27:46heterozygote but it is still there
27:52so what you have after all
27:55is the homozygote
27:58yellow is yellow
28:02and also the heterozygote
28:05as a yellow phenotype
28:10and only the homozygote recessive
28:14is green
28:20now
28:21when you're taking the
28:23progenies the f1 which are heterozygotes
28:28and
28:29you are crossing in between demo you can
28:31do self fertilization
28:35again
28:36one allele from each parent
28:40here
28:41you're going to have the recessive
28:44alleles
28:47here
28:48you're going to have heterozygote
28:51heterozygote
28:53and homozygote dominant
28:57and the green
28:58is
28:59big
29:01the green is back
29:02because
29:04the
29:04two recessive alleles are going to give
29:08you the recessive phenotype the green
29:12so when
29:14two heterozygote plants are being
29:16crossed
29:17the resulting progenies
29:20are going to have a
29:23a green progeny
29:25and
29:26majority are going to be
29:29yellow
29:31so
29:33the recessive phenotype
29:36is
29:37back
29:40this experiment
29:42was really the critical experiment in
29:48mendelian laws
29:50the experiment that i described for you
29:54are directly giving you
29:58two different important laws of genetics
30:03that came from mental experiments
30:06the law of segregation
30:09and the law of dominance
30:13about the law of independence assortment
30:16here mandalay to do
30:18some other type of experiments that will
30:21be described later
30:25so again
30:27in general
30:28the summary of the result of mendel
30:33here with the color of the flower trays
30:39is the flowing
30:42when you cross
30:44a plant with a recessive trait
30:48with true breeding parents which is
30:52purple
30:56and purple flower phenotype is dominant
30:59to the white flower phenotype
31:03all plants are going to have a purple
31:07flowers
31:09but when you have a cross between
31:12the
31:13f1 generation
31:17the white flower
31:19is going to be back
31:24mender's work
31:26was not just a descriptive work about
31:30dominant and recessive
31:32relationships there is much more
31:36into this
31:38throughout his studies
31:41mendel
31:42recognized the
31:44mathematical patterns
31:47of inheritance
31:50from one generation
31:52to the next
31:55mendel did something very very important
31:59he counted
32:02the plants
32:04with each phenotype
32:09he had
32:10real numbers
32:12of each phenotype
32:15counting
32:16is important it's not just as
32:19descriptive
32:20way of looking on recessive dominant
32:25but it's also about
32:28finding
32:30a special ratio
32:32in between
32:34the different traits
32:37the
32:39dominant and the recessive traits
32:42the ratio
32:45between
32:46the dominant versus the recessive on the
32:50f2 generation
32:53was three
32:54to one but that's wrong because
32:58mendel
33:00in his data
33:02never three to one
33:05yet something
33:07around
33:09three to one
33:10he had three point fifteen to one
33:14he had 2.84
33:18to one
33:20so mendel said that although the data
33:24are not three
33:26to one
33:28the data are trying to tell him
33:33three to one
33:36this is a science
33:38many cases the data are not telling us
33:43the full story
33:46and the scientists need to understand
33:50the meaning of the data
33:55this is what statistical analysis is
33:59all about
34:01actually
34:02mental work represent the merging of a
34:07new scientific field
34:10statistics
34:14but still
34:16looking on the published data
34:21may give the impression
34:24that the statistical significance in
34:27mental experiment
34:30is
34:32too high based on the fact that the
34:35sample size which is
34:38not much more than thousand
34:41in most experiments sometimes it's less
34:43than thousand some pes
34:47and when you're looking on the
34:50specific
34:52ratio when you're using this level of
34:56sample size statistically
35:00some people said that well i mean it's
35:02too good to be true
35:06well after all
35:08experiments are
35:10done outside
35:12they can be affected by wind and other
35:15environmental factors
35:19but
35:20here again
35:22mendel repeated his experiments many
35:25many times
35:28but for the report
35:30it shows the experiment that
35:33are
35:34supporting the point
35:36he was trying to deliver
35:39the
35:40three to one ratio
35:44that's what scientists are doing all the
35:45time
35:47repeating their experiments several
35:49times
35:51getting the idea that they are
35:54getting the same type of
35:56direction but then
35:59in the publication
36:01they are using
36:03the best result which make the point
36:06clear
36:08this is
36:10a science
36:12and mandel
36:13was a real scientist
36:17mendel did not just describe his theory
36:22he also
36:24proved his theory with numbers
36:28he actually discovered
36:31the mathematical pattern
36:34of inheritance
36:36the pattern of inheritance was moving
36:39mathematically
36:41with a 3 to 1
36:43ratio
36:44in the f2
36:45generation
36:48it looked on the
36:51phenotype
36:53of
36:54the f2
36:56and from here
36:58it was able
37:00to make a conclusion
37:03on the phenotype of the parents
37:07so mendel did the test course to
37:10understand the genotype of the parents
37:13and of the f1
37:17and the three
37:18to one ratio
37:21in the f2
37:23gave mandel a strong indication about
37:25the genotype
37:27of the parents
37:31so the three to one ratio
37:34was telling the big story
37:37about mendelian genetics
37:41this way it was able to go backwards
37:45and to determine
37:47what how the expected genotypes in the
37:50parents and what is the mathematical
37:53model which is involved with heredity
37:57the gene transmission
38:02i believe that if the only information
38:06we had for mendel was a descriptive work
38:11that would not make such a huge impact
38:15on
38:16genetics
38:18one of the reason that i think so
38:22is because the descriptive information
38:25about
38:26one phenotype that can be changed
38:29in the following generations
38:32which is part of mendel's theory
38:36was published before
38:38as a written description
38:40about an event that took place
38:44thousands years ago
38:49again the bible is a religious book
38:53but if you take the bible story
38:56as an historical evidence
39:00and if you add
39:02to the bible story
39:05today's scientific genetics here in
39:08goats
39:10you can see that
39:13levan
39:14and
39:15jacob's story
39:18is some sort of practical mendelian
39:22genetics in action
39:27overall jacob was able to switch
39:32a dominant phenotype
39:34into recessive phenotype
39:38the only way
39:40to do so
39:42is by making between heterozygotes
39:47and
39:48the bible jacob was able to do it quite
39:50quickly
39:51so he was able to find to choose the
39:56heterozygotes and
39:58to
39:59mate in between them
40:01in a way
40:03that it can get the recessive
40:06phenotype
40:09so uh
40:11how it can take place the shepherd can
40:14identify that or zygotes by some ways no
40:17ways to look for heterozygotes
40:20which have sometimes a distinctive
40:23phenotype
40:24then you can have a good sense for the
40:28outcome of certain meetings
40:30even without understanding
40:34the
40:34mendelian mathematical
40:38pattern
40:41so what i'm trying to say
40:43is that practically
40:46there is a chance that we were using
40:49mendelian genetics
40:51in some situations
40:54well we were quite successful in the
40:56last
40:5710 000 years in developing strains of
41:01animals and plants
41:04so i believe that the practical
41:07mendelian genetics
41:10was out there
41:11well before
41:13mendel
41:15and according to the mendel's
41:19experimental design
41:22and the data chosen for the report
41:27there is a good chance that mendel
41:30understood the rules of genetics
41:34before we did is
41:36crossing
41:37experiments
41:40and his formal publication
41:44is moreover statistical mathematical
41:48formal proof
41:50of what he had realized in the years
41:53that he set up this
41:55experimental
41:57system
41:58started probably with heterozygotes
42:02initially
42:03and try to make them through breathing
42:06and you realize that
42:08is getting green
42:10from two parents which are yellow
42:13and
42:15trying to understand this may help him
42:18to come with the conclusion
42:21even before he was able to do the real
42:25experiment
42:28and there is a something else when we
42:31are talking about already tauri
42:33the idea of james was not clear
42:36at all
42:38but aristotle
42:40the greek philosopher
42:43thought that inheritance
42:46was not some sort of a spirit or emotion
42:51as others suggested
42:54but it's a physical
42:57coming from both parents
43:01well
43:02even here
43:03you can see that there is some
43:07progression
43:09towards
43:10mendel before mendel
43:16mendel's law of hereditary are usually
43:19stated as
43:22the law of
43:24segregation
43:28no blending
43:30one way
43:32or another
43:35the traits are discrete
43:38traits so what make
43:41them is a discrete
43:44unit
43:46engine
43:48when mandel crossed
43:51contrasting
43:53bread yellow
43:55and green seeded
43:57plants
43:59all the offspring
44:01were yellow
44:03green
44:04disappeared entirely
44:08when mendel
44:10self caused the f1 plants
44:14many of the plants add
44:16yellow
44:17seeds
44:18but summit green
44:20seeds so green is back
44:25it was not lost
44:28it is not back as yellow green
44:32but as struggling like
44:35the parent plants
44:39this is a huge finding
44:43the other
44:45law that came from mendelian experiments
44:50is the law of the dominance
44:53if the two alleles are different from
44:56each other in an organism
44:59then one the dominant allele
45:02determines the organism's appearance
45:06and the other allele the recessive
45:09alleles
45:10has no noticeable effect
45:13of the organism appearance
45:16again
45:17if the two alleles are different
45:22so this is the law of dominance
45:26in the f1 plants only yellow sets
45:31facto
45:32was affecting sets color
45:36in those hybrids
45:39yellow set color
45:41was dominant
45:44and green set color was recessive
45:52today
45:53we know
45:56yellow
45:57is a result of an enzyme that can make a
46:01yellow product
46:04fifty percent of the enzyme
46:08is enough to create a yellow
46:12color in the green sets of the layers of
46:17the gin
46:18are mutated
46:20so there is no
46:22active
46:24enzyme
46:26which is produced in those cells
46:29so the green
46:31is coming from the color of the
46:33chlorophyll
46:36that's really
46:38the
46:38general
46:40translation for molecular
46:44point of view
46:46and when we are looking
46:49on
46:50the genes that are involved with
46:52mendelian experiments and some of them
46:57were discovered and cloned and studied
47:02we can see that actually that's the case
47:05in all those cases
47:09so 50
47:10of the wild type product
47:13gave you a wild type
47:16phenotype
47:18one functional allele is enough to give
47:21you
47:22a similar wild-type phenotype
47:26as
47:27to a little do i mean the fact that you
47:30have hundred percent of the product or
47:3450
47:35product
47:36it's not going to change the phenotype
47:39it's the same
47:42and only
47:43if both alleles are not active
47:46their product is not produced at all
47:51and that is the situation you will have
47:54an alternative
47:56phenotype
47:58here you can see the molecular nature of
48:01mutations
48:03and mutated form are simply not active
48:06as compared to the wild type
48:11so
48:12that's something
48:14that
48:15you can see here i mean the gene
48:18function it's mainly enzymes
48:22in one case you can see here it is a
48:25transcription
48:26factor
48:28that's but still fifty percent of
48:32the
48:33product
48:34is enough
48:36to give you the y-type phenotype
48:40so the wildlife phenotype is dominant
48:42over the
48:43alternative
48:44phenotype
48:46which is no gene product is made of the
48:50gene product is not active today we know
48:53about the genes that are involving
48:55medallion trait
48:57in general
48:58we are talking about enzymes and
49:02transcription factors
49:04which 50 of the wild type is enough to
49:08give you
49:09wild type phenotype
49:13mendelian genetics
49:15is relevant also
49:18to some cancers
49:22tumor suppressor genes
49:25are
49:27producing a certain factor
49:30which protect us
49:32from cancer
49:35they're recessive
49:37in their nature
49:40they protect us from cancer
49:43and
49:44usually
49:45you produce the tumor suppressor genes
49:49from both alleles
49:51that's the normal phenotype homozygote
49:54wild type
49:56so this is what we have in
49:59all our cells
50:01in general
50:04but
50:05if we are losing one allele for some
50:08reason
50:09one allele is mutated or inactivated
50:13the heterozygote cell
50:16as a normal
50:18phenotype
50:21muscle transformation
50:23is to take place
50:25from inactivation of one copy
50:29of a tumor suppressor gene
50:32due to the fact that
50:34half
50:35one out of the two wild-type genes
50:39is
50:40still there
50:43and the function of half of the protein
50:48is enough for the normal
50:51phenotype
50:55an evolving
50:57premalignant
50:59heterozygote cells
51:01can become cancer cells
51:04[Music]
51:05when the
51:07other allele
51:09is lost
51:11when both functional copies of the tumor
51:14suppressor genes that has been holding
51:17back the cell from its proliferation and
51:21the cancer phenotype are not active
51:25the
51:26cell is going to be transformed
51:30the loss of heterozygosity
51:33of
51:33suppressor
51:35can lead to the development of the
51:38cancer
51:40this is a classical
51:42mendelian
51:44genetics
51:50mendel
51:52the father
51:53of genetics
51:57he discovered
51:59the
52:00pattern
52:02that occurs as a layers
52:05pass from
52:07one generation
52:09to the next
52:11transmission
52:13genetics
52:14mental drug desegregation
52:18of genes
52:19and their appearance
52:22in the offspring
52:23as dominant
52:26or recessive traits
52:30men deduced that
52:32genes come in pairs
52:36and are inherited
52:38as distinct units
52:42one from each parent
52:45in general
52:48mendel came
52:50with
52:51a pattern
52:53pair
52:55to two singers
52:58two parents
53:03so
53:04mendel
53:05[Music]
53:06completed his experiments
53:11he wrote the paper
53:13a publication
53:15to summarize the information that he
53:18picked up
53:19from his experiments
53:22he read the paper twice february 8
53:26march 8th
53:27in
53:281865 in the meetings of a natural
53:32history society
53:35and
53:37what next
53:40well
53:41nothing
53:43for many years
53:45mendel's work was
53:48ignored
53:50many people never knew of mendel's
53:54innovation
53:56well until after his death
54:01bender
54:02was a genius
54:04but maybe
54:05not a great presenter and a teacher
54:11his original publication
54:14failed to make others to fully
54:17understand
54:19what he had in mind
54:22i've read the english translation of
54:25mendel's paypal
54:27and found that it is very difficult to
54:31understand mandel for mendel himself
54:36on top of this
54:38his written publication
54:41was in german
54:43and many scientists did not read
54:46this language
54:49darwin for example
54:51at the copy of mendel's paper
54:54it was found in his belonging
54:58in a
54:59envelope that was never opened
55:02so darwin never read
55:05this paper
55:06that probably
55:08would give darwin some directions
55:12towards
55:13his own theory
55:17so after reading the original paper
55:20from the perspective of mendel's time
55:25i can realize how difficult it was in
55:29late 19th century
55:32to
55:33understand
55:34the abstraction
55:36of mental theory
55:40so
55:41one of the lesson that we can take from
55:44this is
55:46that it is not enough to come with great
55:49science
55:50that
55:51other
55:53cannot read or understand
55:57scientists need to
55:59use
56:01best method
56:02to present their work
56:07but
56:09reginald
56:10panet
56:12was a better teacher
56:15many years after mendel
56:17he came with a simple statistical
56:20presentation method
56:22to keep track of the allele distribution
56:26in the gamete
56:30with public square
56:32it is easier to understand what mendel
56:36had in mind
56:38so
56:39let's say that you want to start
56:42with mating between heterozygotes
56:47which have both the lids
56:50one is the
56:53yellow
56:54allele the other one is the green only
56:58first
57:00during the gamete formation
57:04the layers are going to be separated
57:10and
57:12this is
57:13according to the law of segregation
57:17that was coined by mendel
57:21now during the
57:23fertilization
57:25the union between the egg and the sperm
57:29you're going to have the following
57:31distribution
57:33of the allele
57:36again
57:37we have heterozygotes that have one
57:41allele
57:43that
57:43is responsible for the
57:46dominant trait
57:49the other allele is the recessive allele
57:53and during the fertilization
57:56you're going to have
57:58them to be joined together according to
58:02the gamete that is used
58:06so what you're going to have after all
58:08[Music]
58:10is
58:11the following
58:12one homozygote dominant
58:15allele
58:17then two heterozygotes
58:20and one homozygote of the alternative a
58:23little
58:26so
58:27what you're going to have here in terms
58:30of the phenotype
58:33the homozygote dominant
58:37you're going to have
58:39two
58:41heterozygotes
58:44and you're going to have one homozygote
58:48recessive
58:51the
58:52recessive homozygote is going to be
58:55green
58:59and the other three
59:01are going to have a yellow phenotype
59:09so this is the three to one ratio
59:12that was found by mendel on
59:16his experiment with one trait
59:20the three to one ratio
59:23is a critical number
59:26that can explain
59:28what is the mechanism that you can reach
59:32there
59:34so the three to one ratio is the
59:37critical information
59:39which is coming from mendel's experiment
59:43and here it is described in a clear way
59:48by the planet square
59:54so here again
59:56we have pearls
59:59in the parents
1:00:01to singers
1:00:03in the gametes
1:00:06and pears
1:00:08in the next generation
1:00:13this is
1:00:14the
1:00:15core
1:00:17of mendelian theory
1:00:24planet square is used to predict the
1:00:27genotypes and phenotypes of the
1:00:30offspring
1:00:32form across
1:00:35with punnett square it is easier to
1:00:39understand what mendel had in mind
1:00:43a gene pair defined
1:00:46each inherited trait
1:00:48parental genes are randomly
1:00:52separated
1:00:53to the gametes so that gamete contain
1:00:57only
1:00:58one gene of the pair
1:01:01and offspring therefore
1:01:04inherit one
1:01:06genetic allele from each parent
1:01:09when success unite
1:01:11in fertilization
1:01:17after mendel completed his work with
1:01:21peace
1:01:23he tried to extend his work to animals
1:01:28so
1:01:29he turned to
1:01:31experimenting with honey bees
1:01:35but he failed to repeat his rules of
1:01:39hereditary
1:01:40and one of the reason
1:01:43was that
1:01:44he was not aware to the fact
1:01:48that in bees the males
1:01:51are haploid
1:01:53the females is deployed but the male are
1:01:56haploid
1:01:58so you cannot see mendelian walls
1:02:02like
1:02:03we add in
1:02:05the
1:02:05peace and in many other
1:02:08organisms including us
1:02:11when male and female
1:02:13are deployed
1:02:16later in 1968
1:02:20he was promoted to become the edit of
1:02:23the monastery
1:02:26and his scientific work
1:02:29largely ended as he became consumed by
1:02:33his increased administrative
1:02:36responsibilities
1:02:39mendel died on january 6
1:02:4318
1:02:4484 at the age of 61.
1:02:48in bruno
1:02:50for many years
1:02:52mendel's work was
1:02:55rejected
1:02:56ignored
1:02:58at that time most biologists
1:03:02held the idea
1:03:04that
1:03:06the blending
1:03:07inheritance
1:03:09is the right type of
1:03:12inheritance model
1:03:16people never knew mendel's innovations
1:03:20until after
1:03:22his death
1:03:28up until the end of the 19th century our
1:03:31understanding of genetics was very
1:03:34limited
1:03:36however
1:03:37since the mid
1:03:391600s
1:03:41or so
1:03:42with the discovery of the microscope
1:03:46we were able to understand that cells
1:03:50are the basic
1:03:52unit of structure
1:03:55in every
1:03:57living things
1:04:00since the microscope was invented
1:04:04scientists were able to see the cells by
1:04:08using some stains
1:04:11dies
1:04:12they tried many different dyes and in
1:04:16sub they found something in the middle
1:04:20of the cell
1:04:22that was stained very well
1:04:27for much of the 19th century
1:04:29scientists had no clue
1:04:32what is the function of this part of the
1:04:35cell
1:04:36that is stained so nicely
1:04:41so
1:04:42what is the first things to do
1:04:44when
1:04:45you see something
1:04:47but have no idea what it is all about
1:04:53well
1:04:55maybe
1:04:56to give this something
1:04:58a strong name
1:05:00and
1:05:01this name
1:05:03chromosome
1:05:04[Music]
1:05:05is
1:05:06actually cuomo
1:05:09zom
1:05:10which in our language can be
1:05:13translated to
1:05:16the colored stuff
1:05:20but those color stuff
1:05:24were found to be
1:05:26quite unique
1:05:28because they know
1:05:30how to dance
1:05:33and they know to dance not one
1:05:37but two different dances
1:05:41one in cells that are in the process
1:05:44to become
1:05:45eggs or sperms
1:05:48the gametes
1:05:50in different dance
1:05:53in all other body cells
1:05:55and this dance that is in all other body
1:06:00cells
1:06:01look like that
1:06:15[Music]
1:06:25scientists
1:06:27really wanted to understand
1:06:30what is the biological reason
1:06:33for the
1:06:35beautiful dances
1:06:38as we all know
1:06:41one represent mitosis
1:06:45and the other one
1:06:47meiosis
1:06:48a necessary process
1:06:51to make egg meat
1:06:54that was the discovery
1:06:57of teldo bovary
1:07:01towards the end of the 19th century
1:07:04suton and bovary
1:07:07carried out a careful observation
1:07:11of
1:07:12meiosis
1:07:14and they formulated
1:07:16the chromosomal theory of inheritance
1:07:22and with this theory of inheritance
1:07:26they found the pattern
1:07:29pear
1:07:31singers
1:07:33pear
1:07:36again
1:07:38the development of sperm and eggs
1:07:41start with a normal cell
1:07:44deployed
1:07:47the egg inserts
1:07:50are
1:07:51haploid singles
1:07:54and the union in between them
1:07:57bring back
1:07:59the
1:08:00diploidity the pair
1:08:02in the following generation
1:08:07so
1:08:08according to their proposal
1:08:12meiosis
1:08:14came with a pattern
1:08:17of inheritance
1:08:19that mendel observed
1:08:23mendel's rules
1:08:25can be explained by
1:08:28independent alignment and separation
1:08:32of homologous chromosomes at meiosis one
1:08:39me all this is a special
1:08:42cell division
1:08:44to make meat
1:08:45sperm and eggs
1:08:49why would regular mitosis
1:08:52be a problem in making meats
1:08:55well i mean we are diploids
1:08:58so let's say that the egg is diploid
1:09:01like the rest of our body sets
1:09:05and the sperm is also deployed
1:09:08and upon fertilization
1:09:11and i mean i'm going to have an embryo
1:09:14with foreign
1:09:16it's not going to be deployed
1:09:19but it's going to have four chromosomes
1:09:22in order to stay as diploid organism
1:09:27that the embryo will stay a diploid
1:09:29organism
1:09:31the egg will be applied the spam to be
1:09:35haploid
1:09:36and the union between the egg and the
1:09:38sperm
1:09:40is going to make a
1:09:43diploid
1:09:44embryo
1:09:46and that's exactly what meal this is
1:09:48about
1:09:51near this is about
1:09:54turning a cell
1:09:55which is deployed
1:09:58into an haploid cell
1:10:02so in the germ cells egg and sperm
1:10:07is essential
1:10:09there is only one copy of each
1:10:11chromosome pair
1:10:13so the meiotic cell division
1:10:16generate cells with half of the genetic
1:10:20material
1:10:22return from two sets of chromosomes to
1:10:25one set of chromosomes
1:10:29so
1:10:31it again
1:10:33pear
1:10:34singers
1:10:36pear
1:10:38that's
1:10:40the mendelian pattern
1:10:42as well
1:10:44two
1:10:45pears
1:10:46singers
1:10:47egg and spam
1:10:50pears
1:10:51in the embryo
1:10:54we can see it here in human being life
1:10:58we start with an organism which is to
1:11:01end deployed
1:11:04during me all this
1:11:06we are making eggs and sperms that
1:11:09are
1:11:10haploid fertilization
1:11:14bring back the diploidity in the embryo
1:11:19and then
1:11:20the embryo is going to stay deployed
1:11:24throughout
1:11:25mitosis
1:11:27and
1:11:28later on
1:11:30the meiosis is going to start the cycle
1:11:34once again
1:11:37so during the sexual reproduction
1:11:40sperm
1:11:42male reproductive cell and an egg
1:11:45female reproductive cells unite to form
1:11:49a new individual
1:11:52a process called fertilization
1:11:56so the sexually reproducing organisms
1:12:01are diploid
1:12:03to end 46 chromosomes in human
1:12:08gametes
1:12:09are formed from
1:12:11germ cells throughout the process called
1:12:15meiosis
1:12:16the gametes formed by myosis before they
1:12:19can be
1:12:21used for fertilization
1:12:23creating the zygote
1:12:25those gametes combine at fertilization
1:12:29to form a zygote which is
1:12:32deployed
1:12:34to an
1:12:3546 chromosomes
1:12:38and one set of chromosomes come from
1:12:41applied egg which is 23 chromosomes and
1:12:45the other set comes from haploid sperm
1:12:48another 23 chromosomes
1:12:53here again
1:12:54per
1:12:56singles
1:12:59bear
1:13:06so
1:13:07me all these feet mentals quite well
1:13:11decades after mendel's death
1:13:15in the early
1:13:1720th century
1:13:20based on the pattern of
1:13:23meiosis
1:13:26several scientists rediscovered
1:13:29mendel's research
1:13:33they probably communicated with each
1:13:35other
1:13:37do you remember
1:13:39the dead monk that was also talking
1:13:43about perv to singles pair
1:13:47like the new study by movie
1:13:52well
1:13:53each of them
1:13:54repeated mendel's findings
1:13:58and came to the same conclusion
1:14:01on their own
1:14:04william
1:14:05betson
1:14:07also
1:14:08translated mendel's paper to make it
1:14:11available for the scientific community
1:14:14that many of them
1:14:16are not reading german
1:14:20so
1:14:21the me of this
1:14:23is pretty much
1:14:26mendel's theory
1:14:28in principle
1:14:31but the correlation between mandel srit
1:14:35juan
1:14:36and meiosis
1:14:38in the pattern
1:14:39of pure singers pair
1:14:44it's not necessarily a full proof that
1:14:47they are
1:14:48indeed
1:14:50the same thing
1:14:53in order to prove the correlation
1:14:57is indeed representing the same idea
1:15:02you need to show that something else is
1:15:06applied from that correlation
1:15:09and can be explained by both set of data
1:15:16and that's actually
1:15:19the
1:15:20type of the scientific application
1:15:25that need to take place
1:15:28in order
1:15:29to nail down the idea
1:15:32that mendel's and bovary
1:15:36data are
1:15:38talking about the same thing
1:15:43and one of them
1:15:45is
1:15:47independent
1:15:50assortment that was one of the
1:15:53application
1:15:54that can help to understand
1:15:57whether bovary and mandela were talking
1:16:02about the same thing
1:16:06so we started with
1:16:09pair of single pairs correlation with an
1:16:12idea that meiosis could explain mendel
1:16:16as
1:16:18it is consistent
1:16:20with mental observation
1:16:25but as correlation is not proof
1:16:29they move further to prove the point
1:16:32with experiments
1:16:36this is type of application
1:16:39in science
1:16:41when data set
1:16:43was combined with other set
1:16:47of data
1:16:51so
1:16:52mendel
1:16:53did experiments
1:16:56with two traits
1:16:59and came with the principle of
1:17:02independent
1:17:04assortment
1:17:08so
1:17:09mender
1:17:10used the hybrid courses
1:17:14mating between parents that are both
1:17:17heterozygote
1:17:19for
1:17:20two traits
1:17:22to determine whether
1:17:24the principle of segregation
1:17:28held true if parents different in more
1:17:33than one trait
1:17:37the loved independent assortment is
1:17:40telling us that genes
1:17:42for different traits
1:17:45are sorted separately from one another
1:17:49so that the inheritance of one trait is
1:17:53not dependent on the inheritance of
1:17:57another
1:18:00so
1:18:01let's see how we can do
1:18:04such an experiment
1:18:07first
1:18:08we are producing
1:18:11an organism which is
1:18:14heterozygote for two threats how to do
1:18:17this
1:18:18one parent
1:18:19is
1:18:20recessive to both traits
1:18:24the other one is two bedding dominant of
1:18:29two traits
1:18:32the cross between
1:18:34the true blade dominant and
1:18:37recessive
1:18:39is going to produce an enterozygote for
1:18:42both the leaves
1:18:45and now
1:18:46you can
1:18:48use the heterozygote for cell
1:18:50fertilization
1:18:53if both alleles
1:18:55are segregated
1:18:56together
1:18:58for example
1:18:59here
1:19:00capital r and capital y
1:19:03are going to be segregated together
1:19:07and small r and small y is also going to
1:19:11be segregated together from this parent
1:19:15and that's going to be the case in the
1:19:18heterozygote the heterozygosity is in
1:19:21both genes but
1:19:24the connection between the
1:19:27capital r and the capital y which comes
1:19:30from here is going to be maintained so
1:19:34you're going to have capital y capital r
1:19:37and the other option will be small r and
1:19:40small y because it is coming from here
1:19:44when it is linked to each other
1:19:47in this case
1:19:48when you're doing self-crossing in f1
1:19:53you're going to have
1:19:54four different options
1:19:57and you're going to have the
1:20:00following distribution
1:20:02means that you're going to have three
1:20:05to one ratio
1:20:09the three are dominant phenotype
1:20:13and
1:20:14the one
1:20:16is the recessive phenotypes for both
1:20:19phenotype
1:20:22that's one option
1:20:25another option
1:20:27is
1:20:28that
1:20:29genes
1:20:30are and why are totally independent of
1:20:33each other
1:20:34so
1:20:35when you get the
1:20:38combination of them they are not really
1:20:41linked to each other in any way
1:20:44if this is correct you're going to have
1:20:47a certain distribution
1:20:50that is going to be
1:20:54in the following way first you're going
1:20:56to have all the different options
1:20:58you can have link between the r and the
1:21:02wide are in the other wide and the small
1:21:05out with the wide small r with the small
1:21:09y so all those different options are
1:21:13here on this planet square
1:21:16they are in the y
1:21:18are not
1:21:19linked to each other
1:21:22and when you are calculating this
1:21:25you can count it
1:21:26you're going to say the following
1:21:30the dominant phenotype of both alleles
1:21:34is
1:21:35in the frequency of 9 out of 16
1:21:39the dominant phenotype in one gene and
1:21:43recessive for the other gene
1:21:46like you see here three
1:21:49and here
1:21:50another three
1:21:52it's three to sixteen
1:21:54the recessive phenotype in both genes
1:21:58is going to appear
1:22:001 out of 16.
1:22:03and according to the experiments
1:22:07we have the ratio of 9 to 3
1:22:10to 3 to 1
1:22:12that means that this option
1:22:16of independent assortment
1:22:19is
1:22:20correct
1:22:22that they are in the why
1:22:25are assaulted in independent manner
1:22:30mendel's results really support this
1:22:33quite
1:22:34clearly
1:22:35this data
1:22:36is consistent with the prediction of
1:22:39independent assortment
1:22:41that we have during
1:22:44the separations of different chromosomes
1:22:49the principle of independent assortment
1:22:52in which a layer
1:22:53of different genes
1:22:55are transmitted independently of each
1:22:58other
1:22:59is supported
1:23:01by mental results with phenotypes of f2
1:23:06offsprings from the hybrid crosses
1:23:11mendel's conclusion
1:23:13was that the two alleles for
1:23:16heretable characters
1:23:19separate segregate during gamete
1:23:22formation
1:23:23independently
1:23:29you can do the two traits experiment
1:23:33with parents of different phenotypes and
1:23:36genotypes
1:23:38as compared to what i showed you in the
1:23:41previous slide
1:23:42here in this animation that i'm going to
1:23:45show you
1:23:47we are going to
1:23:48start with one parent which is
1:23:51heterozygote for both genes
1:23:54and the other parent as the recessive
1:23:58phenotype in both traits
1:24:03to understand the principle of
1:24:04independent assortment let's consider
1:24:07one of gregor mendel's classic crosses
1:24:09in this cross mendel made it a plant
1:24:12grown from a round yellow pea to a plant
1:24:14grown from a wrinkled green pea the
1:24:17offspring of this cross appear in equal
1:24:19proportions of shape and color
1:24:21combinations
1:24:22the wrinkled green parent is homozygous
1:24:25for the recessive r and y alleles and
1:24:27produces only one gamete genotype
1:24:30the round yellow parent is heterozygous
1:24:33big r little r and big y little y for
1:24:36both genes and produces equal
1:24:38proportions of four organic genotypes
1:24:42the gametes fuse with each other in the
1:24:44cross to yield equal proportions of
1:24:46offspring genotypes
1:24:48note that in the gametes from the round
1:24:50yellow parent the dominant r allele is
1:24:53just as likely to be found with the
1:24:54dominant y allele as it is to be found
1:24:57with a recessive y allele in other words
1:25:00the r and y alleles behave independently
1:25:02of each other during gamete formation
1:25:04mendel referred to this independence as
1:25:07the principle of independent assortment
1:25:09today we know that independent
1:25:11assortment is explained by the
1:25:12independent alignment and segregation of
1:25:15non-homologous chromosomes during
1:25:16meiosis
1:25:20these identical diploid cells have just
1:25:22begun meiosis their progress through the
1:25:25cell divisions will illustrate the
1:25:27principle of independent assortment
1:25:29each cell is heterozygous for the shape
1:25:32and color genes one chromosome contains
1:25:35the dominant r allele and the homologous
1:25:37chromosome contains the recessive r
1:25:39allele
1:25:40another pair of chromosomes contains the
1:25:42dominant y and recessive y alleles of
1:25:45the color gene
1:25:46during meiosis the harmonicus
1:25:48chromosomes pair up and migrate to the
1:25:51middle of the cell
1:25:53notice that in one cell the chromosomes
1:25:55containing dominant alleles are lined up
1:25:57on the same side of the cell whereas in
1:26:00the other cell they are on opposite
1:26:02sides
1:26:03this arrangement in metaphase one
1:26:05determines which chromosomes segregate
1:26:07to which pole of the cell during
1:26:09division
1:26:10in the first case the dominant r and
1:26:12dominant y alleles end up in the same
1:26:15cell
1:26:16in the second case the dominant r and
1:26:18dominant y alleles end up in different
1:26:20cells the alleles of the shape gene have
1:26:23segregated from each other independently
1:26:25of the alleles of the color gene
1:26:27this is the basis of mendel's principle
1:26:29of independent assortment
1:26:31in meiosis ii the cells divide again
1:26:34notice that there are equal proportions
1:26:36of gamete genotypes one-fourth our
1:26:39dominant r dominant y one-fourth our
1:26:41recessive r recessive y
1:26:44one-fourth our dominant r recessive y
1:26:47and one-fourth our recessive r dominant
1:26:49y
1:26:50on average half the cells that undergo
1:26:52meiosis will produce the genotype shown
1:26:55on the left and the other half will
1:26:57produce the genotype shown on the right
1:27:00genes located on different chromosomes
1:27:03as in our example always a sort
1:27:05independently it's important to note
1:27:07however that genes located on the same
1:27:10chromosome generally do not
1:27:19the law of independent assortment
1:27:23gene for different traits are sorted
1:27:25separately
1:27:27from one another
1:27:29so that the inheritance of one trait is
1:27:32not dependent on the inheritance of
1:27:36another
1:27:40genetics
1:27:42is about
1:27:44application of basic principles
1:27:48but it's also about critical thinking
1:27:52about existing data
1:27:56besides putting mendel's rules and
1:28:00meiosis together
1:28:04scientists can do something else
1:28:08they can argue
1:28:10that if the connection between mendel
1:28:14and meiosis is correct
1:28:18in some situations mendel's rules must
1:28:22be violated
1:28:25and indeed
1:28:27every violation
1:28:29of mendel's goals
1:28:31led us to better
1:28:34correlation
1:28:36between
1:28:37mendel and
1:28:39meiosis
1:28:44how many traits
1:28:46mendel
1:28:48tested
1:28:51seven
1:28:55how many
1:28:56chromosomes you have in the pea plants
1:29:01seven
1:29:03interesting huh
1:29:06especially as we know
1:29:09that each of the tested trait
1:29:14is located on different
1:29:17chromosomes
1:29:21is this an interesting coincidence
1:29:24or very clever decision
1:29:27mendel did
1:29:30from the original paper
1:29:33i got the impression that mandel was
1:29:36initially interested in more traits
1:29:38up to
1:29:4034 also
1:29:44there is a very good chance that mendel
1:29:48made scientific decisions
1:29:52i'm going to report now
1:29:55about the traits
1:29:58that have a
1:29:59simple pattern
1:30:01independent assortment
1:30:04that the gene happen to be located on
1:30:07different chromosomes and that's why we
1:30:09have this independent assortment
1:30:13and then they'll probably plan later on
1:30:17to do the
1:30:18other
1:30:20traits
1:30:21which
1:30:22deal with more complicated stuff
1:30:27this is science
1:30:29we are following mendel's footsteps
1:30:32since
1:30:33then
1:30:34by trying to understand
1:30:36first the basic rules
1:30:40and to move
1:30:41towards the complicated stuff
1:30:44later on
1:30:46and that's what mendel did
1:30:48it was looking on trades that are
1:30:51located on different chromosomes
1:30:54and in those type of threats well i mean
1:30:57you obviously have an independent
1:31:00assortment because the chromosomes are
1:31:04assaulted independently
1:31:07during meiosis
1:31:12so if mendel is right and if mendel and
1:31:17meoses are describing the same thing
1:31:21mendel independent assortment who
1:31:25must be violated for genes located on
1:31:28the same chromosome
1:31:31they are not transmitted independently
1:31:33of each other
1:31:35but
1:31:36together
1:31:38genes on the same chromosomes are not
1:31:41transmitted independently
1:31:43of each other
1:31:46and in this case
1:31:50mendel and bovary are talking about the
1:31:53same thing
1:31:55in those cases that the rule of
1:31:58independent assortment
1:32:00is going to be violated
1:32:06i can say this
1:32:07even more clearly
1:32:09meiosis fit mendel perfectly well only
1:32:13if in some cases
1:32:16the independent assaultnet go
1:32:19is
1:32:20violated
1:32:22we have thousands of genes on each
1:32:24chromosome if mendel was dealing with
1:32:28trait number eight
1:32:30or more
1:32:33yet to find that
1:32:34his independent assortment rule
1:32:38is violated
1:32:40he probably decided not to go there at
1:32:44that stage
1:32:46maybe to leave this to adele
1:32:49later
1:32:50and that's exactly
1:32:52what took place
1:32:54so we know
1:32:57about the seven traits from mandel
1:33:00and each of those threads
1:33:02are located
1:33:04on different chromosomes so it came with
1:33:07the independent assortment rule
1:33:10leaving the
1:33:11other traits that are working
1:33:14differently
1:33:15aside
1:33:17for now
1:33:20and if mendel is right
1:33:24the violation of independent assortment
1:33:27rule
1:33:29that we just discussed
1:33:31must be violated
1:33:34four jains located
1:33:36on the same chromosomes but are going
1:33:38throughout a genetic recombination
1:33:41during prophase one of meiosis
1:33:46may all this produce one random course
1:33:48over
1:33:51chromosome arm on average
1:33:54and if the genes are on the same
1:33:56chromosome but they are located
1:33:59a bit further apart from each other
1:34:03are not going to be
1:34:05violating
1:34:07the independent assortment rule
1:34:11although they are located on the same
1:34:13chromosome
1:34:15they are transmitted independently of
1:34:18each other
1:34:19in this case they are going to violate
1:34:23the violation of independent assaultment
1:34:27so meiosis fit mentals perfectly well if
1:34:32in some cases the independent associate
1:34:35is applied to genes located
1:34:38on the same chromosome
1:34:42well i'm sure that those of you that are
1:34:45planning to go to law school
1:34:47and to be lawyers have a lot of fun in
1:34:50this lecture
1:34:52and usually
1:34:54rules have exceptions
1:34:56and lawyers like exceptions
1:35:00however
1:35:01as
1:35:02biologists how should we deal with so
1:35:06many exceptions to the rule
1:35:10i would say that
1:35:11the exceptions to mendel's goals is the
1:35:15best things
1:35:16that is happening to those rules
1:35:20let's make mendelian genetics
1:35:23to be the reference of genetics
1:35:27any time the rules are violated
1:35:32we had some
1:35:34explanation to do
1:35:37any violation of mendel's rules
1:35:40help us to understand something new
1:35:44about the complexity of genetics
1:35:49this is the strength of mendel's work
1:35:52not the weakness as many suggested over
1:35:56the last annual years also
1:36:01other violation of mendel's rules
1:36:04different system of their sex
1:36:06determination
1:36:09in human and other mammals there are two
1:36:13varieties of sex chromosomes
1:36:16x
1:36:17and y
1:36:19female
1:36:20is xx
1:36:23male
1:36:25is
1:36:26x
1:36:26y
1:36:28family f two chromosomes of x
1:36:31male f one x one
1:36:34y
1:36:35so here
1:36:36sex
1:36:37linked inheritance
1:36:39is actually also based on mendelian
1:36:42rules
1:36:44and linked them to chromosomal genetics
1:36:48so when it comes to
1:36:51male genetics
1:36:53we need to know that we are haploid for
1:36:55the x chromosome and also for the y
1:36:58chromosome
1:36:59females is diploid for the x chromosome
1:37:03the x chromosome it's a large chromosome
1:37:05they have a lot of genes there
1:37:07and those genes act differently
1:37:10in males and females for their genetic
1:37:14pattern
1:37:16so here we don't have pair singles pair
1:37:20in mail
1:37:22another thing that makes things quite
1:37:24complicated is when you are looking on
1:37:28other
1:37:29animals
1:37:31here
1:37:32we have some changes in the sex
1:37:36determination
1:37:38many animals have different sex
1:37:41determinations
1:37:44the
1:37:45x
1:37:46zero
1:37:47sex determination system
1:37:50is a system that
1:37:52crickets
1:37:55grasshoppers
1:37:56coco chairs
1:37:58and other
1:38:00insects used to determine their sex
1:38:03in this system male have one x
1:38:07chromosome no y
1:38:09while female have two
1:38:11x chromosomes
1:38:14in birds
1:38:17well here the large sex chromosome
1:38:21which is the
1:38:23z
1:38:24is homozygous diploid in male
1:38:27couploid z
1:38:29is
1:38:30female so that's make things a bit
1:38:34more complicated when you're trying to
1:38:37do the analysis it's pretty much the
1:38:40opposite of what you have in human being
1:38:45in a
1:38:46birds the male is homozygote for the sex
1:38:49chromosome and the female is
1:38:51heterozygote
1:38:54in bees
1:38:56males are a haploid
1:38:58for all the chromosomes
1:39:01and female is diploid for all the 16
1:39:04chromosomes
1:39:06and
1:39:07still the application of mendelian rules
1:39:10applies
1:39:11if you know what is the system that you
1:39:14are working with
1:39:17there is one more thing that we learn
1:39:20from
1:39:21mendel
1:39:23and this is
1:39:25a test course
1:39:27a tescos allow us to determine the
1:39:30genotype of an organism
1:39:33with a dominant phenotype but unknown
1:39:37genotype
1:39:39that's involved with causes of an
1:39:41individual
1:39:42with a dominant
1:39:44phenotype
1:39:45with an individual
1:39:47that is homozygous recessive
1:39:50for the trait
1:39:54so
1:39:55the test course is the genetic method
1:39:59we learned from mendel
1:40:01mendel the test process
1:40:04to understand the genotype of the
1:40:07parents
1:40:10so how we are using a test course to
1:40:13confirm a genotype
1:40:16when you have the dominant phenotype for
1:40:18two genes
1:40:20you have different
1:40:22options
1:40:23about the possible genotype
1:40:26so here you have a dominant phenotype
1:40:30for both alleles
1:40:32what is the genotype here
1:40:34so here you have different options for
1:40:38the genotype
1:40:40of the dominant phenotype of both genes
1:40:47so the test course
1:40:48to confirm the genotype
1:40:51of
1:40:52the dominant phenotype
1:40:56is based on using
1:40:58recessive
1:41:00parent
1:41:01the parent which is recessive for both
1:41:04alleles here you know that recessive
1:41:07must be recessive in both alleles so
1:41:11when you have recessive
1:41:13parent you know what is the genotype of
1:41:15this parent
1:41:18and if you find for example
1:41:21that the crossing between
1:41:24this dominant and the recessive
1:41:27p
1:41:28is giving you one to one to one to one
1:41:31ratio
1:41:32in this case
1:41:34you can calculate and figure out
1:41:38that we are talking
1:41:40about
1:41:42dominant which happened to be
1:41:44heterozygote for both genes
1:41:47so in test course
1:41:49a parent that is homozygous recessive
1:41:52for a particular trait
1:41:55is mated with a parent that has a
1:41:59dominant
1:42:00phenotype
1:42:02but unknown genotype
1:42:05the parent with the dominant phenotype
1:42:09maybe
1:42:10homozygote or heterozygote for the trait
1:42:15because the genetic contribution
1:42:19of the
1:42:21homozygote recessive
1:42:24parent is known there is only one option
1:42:27the genotype of the other parent can be
1:42:31inferred from the result of the test
1:42:34cause
1:42:35because the genetic contribution of the
1:42:38homozygous recessive parent is known
1:42:41the genotype of the other parent can be
1:42:44calculated
1:42:46here from the
1:42:48results that we have here
1:42:51and
1:42:52you can
1:42:53get the idea that in order to have this
1:42:56type of distribution
1:42:58you must have
1:43:00that the genotype of
1:43:02this
1:43:03dominant parent must be
1:43:07heterozygote for both
1:43:12gregor mendel
1:43:13challenged the existing general
1:43:15understanding of genetics at that time
1:43:21soy is welcome pay plans as a model
1:43:27it discover the fundamental law of
1:43:30inheritance
1:43:33mental genetics is powerful
1:43:37because of its
1:43:39simplicity
1:43:42but from here
1:43:44we can say that there are
1:43:47much more
1:43:49non-mendelian genetic complications
1:43:53mandel didn't know anything about
1:43:56epigenetics
1:43:59we also have codominance well cases
1:44:03when the phenotype produced
1:44:06is actually produced by both alleles
1:44:10and each of them is clearly expressed
1:44:15furthermore
1:44:16mendel chooses genetic threats in plants
1:44:20that are determined by only two alleles
1:44:25nature
1:44:26genes usually exist in several different
1:44:31form of
1:44:32multiple alleles
1:44:36you can have different mutations on the
1:44:38same gene
1:44:40and each mutation
1:44:42can make things to look a bit different
1:44:46furthermore
1:44:48many polygenic traits
1:44:51that are produced by the interaction of
1:44:55several genes
1:44:57when we are talking about a certain
1:44:59product which is produced by a pathway
1:45:03which is a
1:45:05system that consists of several genes
1:45:09its
1:45:10gene
1:45:11is going to have its effect
1:45:16but again
1:45:18mendelian genetics is our
1:45:22reference and every time they are
1:45:25violated
1:45:26we learn new rules in genetics
1:45:31on top of this
1:45:32mendel came with new scientific
1:45:34approaches
1:45:36his experimental design
1:45:39the way he dealt with his data
1:45:43created new standards in a scientific
1:45:46work
1:45:47and we still following his footsteps by
1:45:51applying those methods to our research
1:45:57mendel was the first one
1:46:00to come with a some sort of statistical
1:46:03analysis
1:46:05to tell that the numbers that are not
1:46:09exactly
1:46:11one two three ratio
1:46:13of telling us that it's one two three
1:46:18mendel was not aware during his life
1:46:22for the youth scientific contribution he
1:46:25made
1:46:26he died approximately
1:46:2925 years before his scientific
1:46:31contribution
1:46:33was
1:46:35recognized

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