Sex Determination in Humans & How to solve sex-linked genetics problems

In Humans: X X = X Y = The X chromosome is a very large chromosome with many active genes. The Y chromosome, however, is very small & has one small active region that is called “the Sex determining Region of the Y chromosome” a.k.a. the SRY.

Sex-Linked Genetics When we talk about traits (genes) that are “sex-linked” that’s genetics code for that gene is located on the X chromosome (and not on the Y).

Sex-Linked Genetics H = normal blood clotting h = hemophilia (a blood clotting disorder) For instance, the gene for normal blood clotting is sex-linked. There are two alleles:

Hemophilia is sex-linked Since it is sex-linked we have to write the alleles on the X chromosome. So the correct way to write this is on the X’s is as a superscript: X H = normal blood clotting X h = hemophilia

How to Solve Sex-linked Genetics Problems 1. Write the letters: The Problem: If a normal woman, whose father was a hemophiliac, marries a hemophiliac man, what are the odds any of their children will have hemophia? X H = normal blood clotting X h = hemophilia 2. Write the cross: X H X h x X h Y 3. Punnett Square: 4. Solve the problem:Each child will have a 50% chance of having hemophilia

Now you are ready to solve some problems on your own…Enjoy!