Question

A woman who has blood type A positive has a daughter who is type O positive and a son who is type B negative. Rh positive is a trait that shows simple dominance over Rh negativeand is designated by the alleles R and r, respectively. A third gene for the MN blood group has codominant alleles M and N.
Which of the following is a possible phenotype for the father?
A) A negativeB) O negativeC) B positiveD) AB negativeE) impossible to determine

Answer 1

Answer:

C) B positive is the right answer

Explanation:

Codominance  

ABO blood group is an example of co dominance. According to this  

Two alleles are both dominant,  So A and B are both co dominant, they will express and I allele which will be recessive.  

Type A-------------- AA or Ai

Type B---------------BB or Bi

Type AB------------- AB  

Type O--------------- ii

Rh antigen is dominant to Rh- (for positive and negative due to presence of Rh antigen  

So for Rh+ = RR (homozygous dominant) and Rr (heterozygous dominant)  

           Rh-= rr (homozygous recessive)

Given conditions in the questions  

Given type                  Alleles for type             Allele for Rh antigen  

Type A Woman A+         Ai                                                Rr

Daughter Type O+          ii                                                 R?

Son type B-                             Bi                                             rr

Father type                          Bi                                           Rr or rr

• As mother is A positive, so definitely the son got his B allele from the father, so father should have allele.  

• So as the daughter is ii, so it means the daughter is getting one i allele from mother and other i allele came from the father  

• As the son have B allele which comes from father, so what is son getting from mother? Definitely he is getting i allele from mother because that the only way mother can donate to the son and not change his blood type.  

• No we know that the son is rr for Rh antigen, which means that he is getting one r from mother because she must have a little r to donate to her son and one r from father

       

The father is either type B Positive BiRr or type B Negative Birr, but we have no other answer than type B positive in the multiple option. This is the possibility