All language subtitles for 47031x_MH_Comp_Inheritance_Patterns_split_04_Comp_X-en

MICHAEL HEMANN: So let's look at another phenotype, another eye

color.

So here we have wild type again.

And we have another eye color that appears.

And this is apricot.

That's a nice name for a fly eye color.

And so what do we know about this apricot allele?

So we know this apricot phenotype is X-linked,

and we know it is recessive.

So we know this already going into this study,

but we want to see-- we want to be able to do a complementation

test and figure out is apricot an allele of white?

Are they the same gene or are they, in fact, different genes?

So how do we do that?

Well, again, we do a cross.

So let's start with more true breeding flies.

And we'll start with a female that

has white eyes, as we did in the past,

and we will cross with a male that has apricot eyes.

And so we're thinking about two different possibilities here.

One is that they're in the same gene,

and the other possibility is that they

are in different genes.

And so let's essentially draw out

those two different scenarios.

There's a question, is it known when we compare mutants

to wild types that the alleles are from the same gene.

So we don't right so we actually have--

that's why we have to do these crosses.

So part of the test is to see whether--

if we have true breeding strains, that is one dominant,

is one recessive.

And here we're localizing these mutations to particular genes

while knowing essentially nothing about the gene

structure itself.

It's really the benefit of the ability

to do this complementation test, the ability

to determine whether they're in the same gene or not.

All right, so let's think about this possibility,

that if they are in different genes.

So if they are in different genes.

So let's start with the female.

And the female, we're going to say, has this white allele

and is wild type for the apricot allele.

So two different genes.

We'll indicate them by essentially a gene, and then

a comma, and then the other gene.

So it's true breeding.

So this female has two X chromosomes

and they're identical.

And we're going to cross with a male that is essentially

wild type.

And just for clarity, we're going

to say w minus and w plus.

So essentially wild type with that white eye

allele and deficient, or a mutation

in that apricot allele.

So we are crossing white eyes to apricot eyes.

And so the progeny of this cross, if you're a female,

is going-- you're going to have an X chromosome that

is w minus A plus, and you're going

to have another X chromosome that comes from the father that

is w plus a minus.

Now the male from this cross is just inheriting a single X

chromosome from the mother, so it's much less interesting.

The males are frequently less interesting here.

It's a common trait that will only

have this w minus A plus and a Y.

It's not telling us anything about the interaction

of these two alleles.

So this is a white eyed male.

And the question is, what is the phenotype of this progeny?

So if they are in different genes,

then we would expect it would complement.

So it would be wild type due to complementation.

So red-eyed due to complementation.

All right, so let's think about the other scenario.

And the other scenario is that they are in the same gene.

So if they're in the same gene, we have a female.

And the female is two X chromosomes.

One is w minus, the other is w minus, true breeding female.

We cross with a male.

That male is apricot minus and Y. We have an offspring,

and an offspring is, if it's a female, w minus a minus

So in this case, we would expect this interaction

to yield apricot eyes, although we're not

entirely sure about the interaction of these two

alleles, if there are two mutant alleles in the same gene.

But this is, in fact, the result of this experiment.

This is what you get.

You actually get offspring that have apricot eyes.

So they are in the same gene.

We've just done a complementation test

for an X-linked gene, and we actually see the--

essentially a restoration of some

phenotype due to the introduction

of this apricot allele.

So the way this generally works is that if you have white eyes,

you have no pigment whatsoever.

You have apricot eyes, you have essentially an allele

that has partial function.

So apricot is an allele, a version of the white gene

that has some pigment, so some function.

And so red eyes as full pigment.

You actually don't know how these

interact with one another.

So the way the experiment done, was

that actually the experiment was done first

and then you went back and thought about the pattern

of inheritance.

And so here, we see that apricot is in fact dominant to white,

that it can actually restore some functionality

in the context of the white background.

But you actually have to do the cross

to be able to interpret the result.

The only way we interpret things like dominant and recessive

are as a result of a cross that we experimentally did.