Question

A gene is found on the X chromosome of humans. A recessive allele leads to loss of the gene function. Using a notation that distinguishes a normal X chromosome and a mutated X chromosome, indicate the genotype of an affected male, a normal male, an affected female, a normal female who carries the mutation, and normal female who can have all normal sons. Try the same exercise for a mutated allele that is dominant over the normall allele.

Answer 1

Case 1: A recessive allele leads to loss of the gene function.
XA – normal X chromosome
Xa - mutated X chromosome
The genotypes :
46XaY – affected male
46XAY – normal male
46XaXa – affected female
46XAXa – normal female who carries the mutation
46XAXA - normal female who can have all normal sons
Case 2: A mutated allele that is dominant over the normall allele.
Xb– normal X chromosome
XB - mutated X chromosome
The genotypes :
46XBY – affected male
46XbY – normal male
46XBXB – affected female homozygote
46XBXb – affected female heterozygote
46XbXb - normal female who can have all normal sons