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CBSE - X - Biology - Heredity and Evolution


Asked by sivakumars 20th March 2010, 9:28 PM
Answered by Expert


No it is not enough.

This information is insufficient to determine the dominant blood group. During cross breeding, even recessive traits can express themselves phenotypically. For example, if a heterozygous male AO mates with OO female, then there is a probability of the child inheriting OO genotype. So, you cannot determine the dominant blood group in this case.

The ABO blood type is controlled by a single gene with three alleles: i, IA, and IB. The IA allele gives type A, IB gives type B, and i gives type O. As both IA and IB are dominant over i, only ii people have type O blood. Individuals with IAIA or IAi have type A blood, and individuals with IBIB or IBi have type B.  A type A and a type B couple can also have a type O child if they are both heterozygous (IBi,IAi).


So in case of a heterozygous male with IAi genotype marrying a ii genotype female, the child has a probability of inheriting ii phenotype, which results in O blood group.

Parents                      IAi  (Father)                             ii (Mother)

Gametes                     IA and    i                                 i 

So daughter could be  IAi   i.e. blood group A or   ii  i.e blood group O. 

The A blood group is actually dominant over O, but here we cannot determine the dominancy based on the given information.

Answered by Expert 21st March 2010, 3:58 PM

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