There are three alleles for the ABO blood group in humans. Why are there only two alleles normally present in any individual? 1. The alleles for the ABO blood group always segregate independently during meiosis.
2. Each parent contributes only one allele for the ABO blood group to the offspring
3. Every gene for the ABO blood group must be recessive.
4. The alleles that determine the ABO blood group are on the X-chromosome.

2. Each parent contributes only one allele for the ABO blood group to the offspring

Explanation:

Humans are diploid organisms, which means that our cells have two copies of the same gene. These copies are called alleles. We inherit one allele from each parent.

Just like most of our traits, we inherit our blood group from our parents. There are three alleles that determine our blood group: A, B, and O. We can get only two of them, though. Whether our blood group is A, B, AB, or O will depend on the combination of the alleles we inherited.

the correct option is option d