Answer to Question #145483 in Genetics for Vaith

Question

A gene of curly hair structure dominates over a gene of straight hair structure and hemophilia is X-linked recessive disease in a human. A healthy woman with curly hair got married to a healthy man with straight hair. They had two children: a hemophilic son with curly hair and a healthy daughter with straight hair. Determine the genotypes of the parents and their children. Determine the probability of birth of a healthy son with straight hair structure

Answer 1

Let Hs represent straight hair and Hc represent woman with curly hair.

Parents genotype: H^s and H^c.

Parents phenotype: (1) Curly hair woman, (2) Straight hair man.

Children genotype: H^sH^c and H^cX.

Children phenotype: (1)Hemophiliac son with curly hair, (2) Normal daughter with straight hair.

If F2 generation is produced, then ½ of daughters will have straight hair and ½ of sons will have curly hair. Males only have one x chromosome hence they will express a recessive trait if there is only x chromosomes has the recessive allele. Hence the probability of birth of a healthy son with straight hair structure is 0.5.