Question

The ABO blood group has three alleles ( A, B, O) where A and B are codominant and O is recessive. If a man with type O blood mates with a woman with type A blood, the expected proportion of heterozygotes among their offspring is ________ depending on the genotype of the woman.

Answer 1

If a man with type O blood (genotype ii) mates with a woman with type A blood, the expected proportion of heterozygotes among their offspring is 100% if the woman is homozygous (AA) and 50% if she is heterozygous (iA).

Step-by-step explanation:

The ABO blood group system is a classic example of codominance and multiple alleles in human genetics. In this system, the alleles IA (or A) and IB (or B) are codominant, meaning that both alleles are fully expressed when present. The allele i (or O) is recessive and does not encode for any protein on the red blood cells. If a man with type O blood (genotype ii) mates with a woman with type A blood, and if the woman is heterozygous (iA), all their children will receive one i allele from the father and can receive either an i or an A allele from the mother. This scenario results in a 50% chance that the offspring will be heterozygous (iA, which is blood type A). However, if the woman is homozygous for type A (AA), all children will be heterozygous (iA) since they will get one A allele from the mother and the i allele from the father. Therefore, the expected proportion of heterozygotes among their offspring is 100% if the woman has genotype AA, and 50% if she is genotype iA.