the blood group is determined by a gene I which has three form or allels viz ,IA,IB,IO the genes IA and IB are dominant to IO but how can you explain the appearance of blood group AB in the following punnet square
Answers
Answer
Human blood group inheritance is the example of codominance and multiple alleles. It is governed by three alleles namely I
A
, I
B
and I
O
. I
A
and I
B
show codominance while allele "I
O
" is recessive to both "I
A
" and "I
B
". Since each allele can combine with any of three alleles, this gives total six genotypes I
A
I
A
, I
A
I
O
, I
B
I
B
, I
B
I
O
, I
A
I
B
and I
O
I
O
. Thus, option A is wrong.
Since, I
A
and I
B
alleles are dominant over I
O
allele; the genotypes I
A
I
O
and I
B
I
O
gives A and B blood group respectively. Genotypes I
A
I
A
, I
B
I
B
, I
A
I
B
and I
A
I
B
show A, B and O blood groups respectively. Due to codominance of "I
A
" and "I
B
” alleles, the genotype "I
A
" and "I
B
" produce “AB” blood group respectively.
Thus the six genotypes give total four phenotypes, this makes options C and D wrong. Thus, the correct option is B.