Question

You will use A, B, and O for these questions to represent the alleles in this example.

The ABO blood system works in a Mendelian fashion, but has 3 possible alleles at one locus (A, B, and O alleles). Each person can have only 2 of those alleles in their genotype. A and B are both dominant (and so can be co-dominant), and O is recessive to both A and B. So, for example, if you have B blood type, your genotype could be either BB or BO -- both of those genotypes would yield B phenotype. If your phenotype is AB blood type, then your genotype is AB.

Given the following scenario determine the genotypes of all these individuals. (Hint: What can the offspring tell you about the parents?)

You have a mother who has two children. There are two men who might need to pay child support; we need to figure out which man owes. Who is the father of these two children?

Mother: blood type A

Child 1: blood type O

Child 2: blood type A

Possible father 1: blood type A

Possible father 2: blood type O

List all possible genotypes for each of these individuals (mother, 2 children, 2 men).

Based on this information, is it possible to exclude either of these men as being the father? Why or why not

Answer 1

Mother has to be hetrozygous A type , because one of the offspring is O - type. O- recessive allele has to be inherited from both the parents.

Genotype of mother has to be AO. But the genotype of father can't be firmly said because AO (A type) and OO (O type) both types can give rise to offspring with A and O types of blood. But father also can't be AA (homozygous A type ) because one of the offpsring is O type.

As the above punnet square is showing, A type of offspring can be AA / AO. But O type offspring will be OO.

We will not be able to firmly say if heterozygous A type or homozygous O type individual is the father of the children. Because both genotypes can produce offspring with A and O type of blood.

Father can be heterozygous A type or homozygous O type.