Sex Linked Genes and Dominant Genes

Sex Linked Genes

This ties in with reproduction. The 23rd pair of chromosomes has either a Y chromosome and a X chromosome or two X chromosomes (in most cases.) If you are a boy you have an X chromosome and a Y chromosome. If you’re a girl you have two X chromosomes.

This is important because some genes are carried in the X chromosome but not in the Y chromosome like baldness.

Four possible babies can grow depending upon which baldness genes are in the sperm and egg cells that form the zygote.

To understand how each of these possible zygotes could be formed first look at the mother’s donation for each case, then the father’s.

Cases 1 and 2 will be girls that are carriers of the baldness gene, but not bald. Cases 3 and 4 will be boys with no baldness genes.

The Mother's Donation is...

X
without a bald gene

X
without a bald gene

The Father's Donation is ... X
with a bald gene
1)
X^nonbald     X^bald
2)
X^nonbald   X^bald

Y 3)
X^nonbald
Y
4)
X^nonbald   Y

In this picture it shows only the girls get the baldness gene. Since baldness is recessive they are only carriers. They are not bald.

Continue to the next generation