AP Biology 2.2 Essential Life Process Information
AP Biology 2.2 Essential Life Process Information. What is the probability that their son will have hemophilia?
|AP Biology||Essential Life Process Information|
|Change in Genetic Makeup||Phenotypic variation and fitness|
|Test Prep||AP Biology|
have hemophilia? And here are our potential answers…[mumbling]
Okay, let's break it down… Hemophilia is an X-linked, recessive trait.
…What does that mean? Unfortunately, it has nothing to do with the [Two men dressed in X-men costumes]
X-Men. Though that sounds like a good idea for the next sequel…X-Men: Recessive Trait. [Girl watching X-Men: Recessive Trait in an empty cinema]
We'd watch it...just us? Anyway, X-linked means that the gene encoding
the trait is on the X chromosome. And remember that a recessive allele will
not show its phenotype if it's paired with a dominant allele.
So if hemophilia is X-linked and recessive, the picture looks a little more like this…
But what makes a sex-linked gene special, compared to all of the other genes out there? [Chromosome and gene stood together]
Well, besides the fact that all genes are special in their parents' eyes…
Sex-linked genes are exactly what the name says: sex-linked.
So when a mother makes her eggs, half of them will carry the diseased chromosome. [Woman with two chromosomes]
Now let’s take look at the father. He can either pass down a dominant allele
linked to the X chromosome, which would guarantee a healthy female offspring…
Or he could pass down a Y chromosome, guaranteeing a male offspring. [Man passing down a Y chromosome]
But since the hemophilia gene is on the X chromosome, a male offspring only has one [Boy opening a wrapped gift]
chance to get it right? And that chance comes from…?
Bingo. Mommy dearest. So the chances he’ll get the recessive gene
from his mom are… B, fifty percent.
That’s what makes sex-linked genes special. Because male offspring are haploid for the [Parents stood with their son]
X chromosome, all traits on the X chromosome, which come from the mother, are expressed. [Woman with an X chromosome]
Because of this, most X-linked disorders are more common in males than females.
Which could also explain why more of the X-Men are male than female but...don't quote us [X-Men characters in a park]