All language subtitles for 87031x_PR_Laws_Inheritance_06_Mendels_2nd_v1-en

PETER REDDIEN: So now what I'm going to do

is go through this-- we're going to go

through the same exercise we just went through of ascribing

genotypes for these crosses, but now considering these two gene

ideas.

So our first starting strain, then,

would be homozygous for both genes.

I'm going to separate the two genes in my notation

here with a semicolon, like that.

So it would be para ts over para ts shibire ts over shibire ts.

Now we'll cross it to the wildtype.

Homozygous for wild-type alleles of both genes.

We come to our F1 and we inherit one allele

of each gene from each parent.

So we'll be heterozygous for the para gene

and heterozygous for the shibire gene.

And we'll cross F1 siblings to one

another, which is just every sibling has

the same genotype here.

So far so good?

Any questions?

OK, all right.

Now we need to think about our predictions

for the F2 generation.

And to make our predictions for the F2 generation,

we're going to use Mendel's second law, this law

of independent assortment.

And this states that allele pairs of different genes,

the paralyzed gene and the shibire gene,

are different genes assort independently

during gamete formation, meaning which

allele you get for this gene during production of a sperm

or egg has no impact on which allele you get for this gene.

Now I put the qualifier that this

is for unlinked genes, which we'll

come back to in the next lecture what that means.

But for now, let's just work with this simple case

of independent assortment.

Question?

STUDENT: Do these genes have to be on different chromosomes

or can they be on the same one?

PETER REDDIEN: OK, so the question was,

do these genes have to be on the same chromosome

to show independent assortment or can they

be in the same chromosome?

If they're on different chromosomes,

then they will show independent assortment.

If they're on the same chromosome

and they're far enough apart, greater

than what will be called 50 centimorgans apart, as you'll

learn about next lecture too, then you will also see--

can also see independent assortment.

Other questions?

OK.

So now how do we think about the expected outcomes here?

Well, we can think about, like we did last time,

our F1 gametes.

What should they be?

Well, we could get a para ts allele and a shibire ts

allele, one possibility.

We could get para ts shibire wildtype para wildtype

shibire ts and then finally para wildtype shibire wildtype.

OK.

So those are F1 gametes.

What should their frequencies be?

Anybody?

Yeah.

STUDENT: They're all equally likely.

PETER REDDIEN: All equally likely.

So if you randomly sampled, what would the probability

of getting this first one be?

STUDENT: 0.25

PETER REDDIEN: 0.25.

OK, so this will exist in a one to one to one ratio.

So the probability of each, 0.25.