Polydactyly (extra digits) is a dominant trait caused by gene P, as opposed to t
ID: 6263 • Letter: P
Question
Polydactyly (extra digits) is a dominant trait caused by gene P, as opposed to the normal allele p. Cystic fibrosis, c, is a recessive disease as opposed to the normal condition, C. A polydactylous woman, otherwise normal in phenotype, married a healthy normal man. Their four children have the following phenotypes:Child 1: normal in all respects
Child 2: is polydactylous, otherwise normal
Child 3: has cystic fibrosis, otherwise normal
Child 4: has cystic fibrosis and is polydactylous
a) what is the genotype of child 4
b) what is the chance that child 1 is heterozygous for cystic fibrosis
Explanation / Answer
If we already know that the child doesn't have Cystic fibrosis, then we can eliminate the chance of him having cc, so there are only 3 possible allele combinations. (PpCC, PpcC or, PPCc) Two of those are heterozygous. (PpcC and PpCc) Therefore, he has a 2/3 chance of being heterozygous for cystic fibrosis.