He does not pass on his y chromosome to his daughter: a male is affected with the x-linked recessive condition hemophilia. The father"s status is unimportant because he does not pass his x-chromosome on to his male offspring: a woman is the offspring of a father with the x-linked recessive condition hemophilia. The woman must be a carrier so there is a 50% chance she will pass on the mutant allele. There is also a 50% chance her child will be male: the ability to roll the tongue is controlled by a single gene with two alleles. The allele for being able to roll is dominant over the allele for not being able to roll. 10,000 individuals there are 7400 tongue rollers and 2600 non-rollers. Pku allele lack the ability to properly breakdown the amino acid phenylalanine. Build up of phenylalanine causes mental retardation in the children born with pku.