All language subtitles for 67031x_PR_Conditional_Prob_01_Pedigree_Assumptions_-en

PETER REDDIEN: So let's dive in and look

at an example pedigree.

And I'm going to say that we're looking at a rare trait here.

First thing we can do is try to determine

whether we can decipher the mode of inheritance of this trait.

And you can just walk yourself through each of these scenarios

and see if they're consistent with these data.

So let's say, could it be autosomal dominant?

We couldn't explain this individual passing on the trait

if it was autosomal dominant and not showing the trait.

So no.

Autosomal recessive?

This data is not consistent with autosomal recessive

because this individual, we're assuming,

does not bring in an allele.

So this individual could not have an affected offspring

if it was autosomal recessive.

What about X-linked dominant?

Let's think about that.

So let's say, she was heterozygous for it.

Then you'd have half and half.

So you could still be OK.

Then let's walk through the next generation.

So then, what would this person's genotype be?

Would this person inherit the affected allele

or the unaffected allele from this father?

We're doing X-linked dominant.

And this individual is unaffected.

So it would have to get the unaffected allele

from this father.

We can rule this out.

Now X-linked recessive.

It's our last choice.

Let's just try this by mapping a prospective genotypes

onto this pedigree.

So we'll give an X little a allele and an X big A allele

to indicate the alleles of this gene.

So let's start with the first parent.

So this individual would be X little a, X little a.

This individual would be X big A Y, because he's unaffected.

So we'd have X little a Y. And we'd

have X little a X big A. This individual is

coming from outside the family.

So X big A, X big A. So we have Y and X big A.

This individual will be X big A and X little a.

This individual X big A and Y. Then we

have X little a Y, X big A Y. And then

we have this individual.

I'm going to call this individual individual K.

Do we know individual K's genotype?

No.

But we can see that our data is consistent

with X-linked recessive mode of inheritance.