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Multiple alleles and co-dominance
Concepts tested here
- ABO blood groups 2
All Questions
2010 AIPMT-MAINS 1 question
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ABO blood grouping is controlled by gene I which has three alleles and shows co-dominance. There are six genotypes. How many phenotypes in all are possible?The gene I has three alleles: $I^A$, $I^B$ and i. $I^A$ and $I^B$ are dominant over i and co-dominant with each other.
Genotypes $I^AI^A$ and $I^Ai$ give blood group A.
Genotypes $I^BI^B$ and $I^Bi$ give blood group B.
Genotype $I^AI^B$ gives blood group AB, and genotype ii gives blood group O.
So the six genotypes give four phenotypes: A, B, AB and O.
2010 AIPMT-PRE 1 question
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ABO blood groups in humans are controlled by the gene I. It has three alleles – $I^A$, $I^B$ and i. Since there are three different alleles, six different genotypes are possible. How many phenotypes can occur?$I^A$ and $I^B$ are completely dominant over i, and they are co-dominant with each other.
The six genotypes are $I^AI^A$, $I^Ai$, $I^BI^B$, $I^Bi$, $I^AI^B$ and ii.
$I^AI^A$ and $I^Ai$ both give blood group A.
$I^BI^B$ and $I^Bi$ both give blood group B.
$I^AI^B$ gives blood group AB (both antigens expressed) and ii gives blood group O.
So four phenotypes are possible: A, B, AB and O.