Question

A child has blood group O. If the father has blood group A and mother blood group B, work out the genotypes of the parents and the possible genotypes of the other offspring.

Answer 1

Mendel conducted artificial pollination or cross-pollination experiments using several true-breeding pea lines A true breeding line is one that having undergone continuous self-pollination, shows the stable trait inheritance and expression for several generations.

Complete answer:
Mendel selected a total of 14 true-breeding pea plant varieties, such as the height of the stem whether tall or dwarf as pairs which were similar except for one character with contrasting traits. It means, Mendel selected 7 characters that are seed shape, seed colour, pod colour in pea plant for carrying out hybridization experiments and to study inheritance
Mendel crossed pea plants say for example stem height and cross tall and dwarf plants and got ration
3:1 but some inheritance differs from this ratio as:

ABO blood group is a perfect example of codominance.

For ABO system of blood groups, allele A produces N-acetylgalactosamyl transferase enzyme which recognises H antigen present in RBC membrane and adds N-acetylgalactosamine to sugar part of H antigen to form A antigen. The allele IB produces galactosyl transferase enzyme which adds galactose to the sugar part of H antigen to form B antigen. The alleles 14 and 15 produce a slightly different form of the sugar while allele i does not produce any sugar or antigen. IA and I are completely dominant over i, in other words when IA and i are present only IA expressed as i does not produce any sugar, and when IB and i are present, only 1B expresses. When both IA and I are present in a person, both enzymes or sugars thus both antigens A and B are produced. This is because of codominance. These antigens determine the type of blood group. Blood group A have antigen A, group B have antigen B, AB have both antigens while blood group O do not carry any antigen.

Child must be with an O blood group; it is required that both parents should contain at least one copy of the allele. This exactly means parents with A and B blood groups are heterozygous and have genotype IAi and IBi respectively. Parental genotypes IAi and IBi give progeny with IAIB: IBi: 1 IAi: I ii genotypic ratio.

Note: Besides incomplete dominance, certain alleles show codominance. Here in F1, hybrid both alleles express themselves equally and there is no mixing of the effect of the both alleles, therefore hybrid progeny (F1) resembles both parents.