Chapter 13, Problem 11STP

Summary Introduction

To explain:

The chance of having a hemophilic son from a hemophilic father and a carrier mother.

Introduction:

Genetic disorders result from inheritance of traits which are either dominant or recessive. Traits that are controlled by genes located on sex chromosomes; X chromosomes in particular are called sex- linked traits or X- linked traits.Hemophilia is a sex- linked recessive disorder caused by a lack of blood clotting agent called factor VIII.

Answer to Problem 11STP

When a mother is a carrier of the gene, and father suffers from hemophilia;

There is 50% chance that son will also carry the gene and express it.

Explanation of Solution

Traits that are controlled by genes located on sex chromosomes; X chromosomes in particular are called sex- linked traits or X- linked traits. Since males have only X chromosome, they are affected by recessive X- linked traits more often than females. Females usually do not express the recessive trait as other X chromosome will mask the effect of the recessive trait.

According to the given information, father is hemophilic but mother is a carrier of the trait. The genotypes of the offspring can be checked with the help of a Punnett square.

Let X^H= Normal

X^h= hemophilia

Y= Y chromosome

The mother is a carrier of thedisease so she has the recessive allele for hemophilia on one of her X chromosomes. The father is hemophilic so he has the recessive allele on the X chromosome.

	Xh	Y
XH	XHXh	XHY
Xh	XhXh	XhY

Out of the two sons, only one son will have hemophilia as he receives the recessive allele from his mother. So there is 50% chance of a boy to have hemophilia.