Question

With respect to genetics, ABO blood types are controlled by asingle gene designated I, which has three alleles. The I A allelegives blood type A, I B gives blood type B, and i gives blood typeO. The I A and I B alleles are codominant and i allele is recessiveto both the I A and I B alleles.

Aside from the I alleles, there are two other genes that whenmutated affect ABO blood type inheritance. The first mutant isrecessive to wild type and is designated x. A homozygous xxindividual is phenotypically O for blood type no matter what thegenotype is of the I gene. For example, I A /I A x/x or I B /I Bx/x individuals are O type. The second mutant, is dominant to thewild type Y allele and is designated Yd . An individual carrying aYd allele is phenotypically blood type O no matter what thegenotype is of the I gene. For example, an I A /I A Y/Yd or I B /IB Y/Yd individuals is O.

a. Propose a biochemical model that explains the O phenotype ofthe recessive homozygous xx individual? Your model should explainthe biochemical function of the X gene in a wild type individualand should explain why the x mutation is recessive