Answer:
1. No, you can conclude who the father is
2. Yes, man#1 can be excluded
3. A DNA paternity test can be done as a confirmatory test.
Explanation:
The ABO blood group is a system of grouping blood and it depends on the A, B or O gene found on chromosome 9, inherited from each parent. A and B genes are dominant genes (a dominant gene is one that is expressed phenotypically in a heterogenous state), while O gene is recessive (only expressed phenotypically in a homogenous state). Following this explanation, the possible blood groups (phenotype) can be gotten as follows:
1. Group A: A and A or A and O
2. Group B: B and B or B and O
3. Group AB: A and B
4. Group O: O and O
Since her mother's blood group is A and her blood group is AB, it means that the father should either have a blood group of B (genotype B,O or B,B), or a blood group of AB (genotype A,B) so that when crossed with the mother's group A (genotype A,O or A,A), at least one A and one B gene in the parent's genotype can combine to give the A,B group of the young woman. This probable possiblity makes it difficult to conclude who the father is as he can either be man#2 with group B (genotype B,B or B,O) or man#3 with goup AB9Genotype A,B).
Considering the Rhesus factor, (the Rhesus grouping can either be negative or positive, depending on the presence or absence of Rhesus D, antigen on the surface of red cells), it is not possible to determine who the father is because a rhesus negative or positive father (Man#2 or 3) combining with a rhesus positive mother, can produce a rhesus negative child which is the case of our subject.
We are certain that man#1 is not the woman's father because he is group O negative. Being group O, it means that his genotype must be O,O, meaning that the B genotype is absent in when crossed with the mother's A,A or A,O genotype completely disqualifying him as the father of the girl.
Finally, to confirm who the father really is between men# 2 or 3, a DNA paternity test is carried out.
The DNA paternity testing use DNA profiling method to determine similarities between the gene of a child and the parent, by comparisons of the DNA sequence of the child and the parent. For two individuals that are related, the patterns and distributions of the DNA sequence is similar among the individual some sequences may even be copied verbatim, but it differs distinctly in unrelated individuals.
