All language subtitles for 57031x_MH_Inferring_Patterns_05_Xlinked_Dom_Other_v-en

MICHAEL HEMANN: Here's a pedigree of Fragile X syndrome.

Now, Fragile X syndrome is an X-linked dominant condition.

The severity tends to be less in females than males,

but it still represents or appears

as a dominant condition.

So we can see it's dominant because it's

present in every generation.

So it has this dominant trend of inheritance.

And one of the ways that you can actually

tell that this is an X-linked dominant condition, the males,

like this male that's affected, will always

have affected daughters because they will always

inherit an affected allele from the father.

So the father only gives a single X allele,

and if it's a dominant condition,

that will always manifest in a daughter with two X's.

We see seven children that are the offspring of affected

fathers.

And all of the daughters are affected.

Now, whether this is definitive evidence

that this is X-linked dominant or not would depend on what?

How could we actually figure out whether this

is X-linked dominant or is the inheritance

pattern consistent with autosomal dominant?

How would we do that test?

Chi-square, right?

So if it were autosomal dominant,

we'd expect half of these daughters to be affected.

If it's X-linked, we'd expect all of them.

But we would do the kind of chi-square test

that we talked about last time to figure this out.

So there are, of course, other modes of inheritance.

This is an example of mitochondrial inheritance,

where the alteration that's relevant

is actually in the mitochondrial genome.

Here, affected mothers always pass it on to their children.

And affected fathers, because they

aren't passing on mitochondria in sperm,

never pass it to their children.

So it has this sort of characteristic pattern, where

all the progeny of affected females are affected,

and none of the progeny of affected males.

And there are also different cases,

like there's Y-linked inheritance that

would be the same.

These tend to be rare conditions,

but again, they are part of characteristic patterns

of inheritance that you can recognize doing this kind

of pedigree analysis.

And again, we do statistical tests and statistical analysis

to determine whether our hypothesis, given

a particular pattern of inheritance, can be true

or can be excluded by the data.