$\quad$ ABO blood groups in humans are controlled by the gene I. It has three alleles…
$\quad$ ABO blood groups in humans are controlled by the gene I. It has three alleles $-\mathrm{I}^{\mathrm{A}}, \mathrm{I}^{\mathrm{B}}$ and $\mathrm{i}$. Since there are three different alleles, six different genotypes are possible. How many phenotypes can occur?
Three
One
Four
Two
Solution
In ABO blood group system, inheritance of grouping is controlled by a single autosomal gene on chomosome 9 with three major alleles $\mathrm{A}, \mathrm{B}$ and $\mathrm{O}\left(\mathrm{I}^{\mathrm{A}}, \mathrm{I}^{\mathrm{B}}\right.$ and $\left.\mathrm{I}^{\mathrm{O}}\right)$. The $\mathrm{ABO}$ blood group system has at least 6 genotypes. On the basis of presence or absence of antigens and antibodies, four blood groups (phenotypes) have been differentiated-A, B, AB and $O$ blood groups.