All language subtitles for 47031x_MH_Inferring_Patterns_04_Xlinked_Rec_v2-en

MICHAEL HEMANN: So we went over dominant and autosomal

dominant.

We went over autosomal recessive.

This is a trait that is actually an X-linked recessive trait.

In this case, hemophilia, so the absence

of blood clotting or insufficient blood

clotting following a wound.

It can be a life-threatening condition

if people suffer injury.

This is the British royal family.

So you can see Queen Victoria, who--

Queen Victoria in the middle on top of the pedigree

was actually a carrier for hemophilia.

And as you can see in this family,

it is X-linked recessive, and so only males

are affected, because males only have a single X chromosome.

So generally in this context, females are typically

unaffected, males are affected.

If a female is homozygous, then they would be affected,

but that rate is quite low in the context

of X-linked recessive diseases.

For X-linked recessive traits, if the mother is a carrier

and the dad is unaffected--

so if mom is a carrier and dad is unaffected,

then basically half of the sons are going to be affected

and half of the daughters are going to be carriers.

Now affected sons always inherit the allele from the mother.

So in these pedigrees, frequently you'll

see that maternal uncles are often affected.

And dissimilar from recessive traits,

generally consanguinity, or inbreeding,

doesn't really affect incidence.

Because here we're not looking to homozygose

a particular allele.

We have a single allele that's segregating in these families.

And so it's really just the appearance

of this allele in combination with the Y chromosome

or in the absence of a dominant allele

that you actually see these phenotypes.

So inbreeding is not really the cause of--

or doesn't really underlie the appearance of these traits,

and so generally in these pedigrees,

you won't see signs of consanguinity

as characteristics of this.