Assume the disease in the pedigree opposite follows the Mend

Assume the disease in the pedigree opposite follows the Mendelian rules of inheritance and that there is complete penetrance. Is the disease likely to be due to a dominant or recessive allele? Give one reason for your answer. What is the most likely genotype of the II-2 individual? (Use A and a for the dominant and recessive alleles, respectively.) X-linked ichthyosis is a rare, recessive skin disease. A phenotypically normal couple have an affected son and a phenotypically normal daughter. What is the probability that the daughter carries a single copy of the mutant allele?

Solution

1. (a) In the given pedigree, the disease is likely to be due to a recessive allele. This is because none of the parents have the disorder and that they can be heterozygous. The disease was only revealed in one offspring.

2. In the given problem, let A be dominant allele and a be recessive allele. So, here both the genotypes of the mother and father are Aa since they have a affected son and an unaffected daughter. So they have to be heterozygous. Therefore, the affected son has the genotype AA and the unaffected daughter has the genotype Aa. So there is 100% probability that the daughter carries a single copy of the mutant allele.