And in Part D, if the couple has two children, what is the probability that both of them are normal? Now, before we actually examine A through D, let's determine what the genotype is of each one of our parents. So let's begin with the heterozygous normal female. Now, remember, the female contains two X sex chromosomes. So let's designate those X sex chromosomes with the following picture. So, we have the first Xx chromosome and the second X chromosome.