Gene I interacts with gene D to determine the blood phenotypes of humans. Gene I
ID: 226213 • Letter: G
Question
Gene I interacts with gene D to determine the blood phenotypes of humans. Gene I is the gene for ABO blood phenotypes in humans, and includes three alleles: I^A, I^B and i. Gene D includes two alleles. Allele D is dominant over allele d. In individuals homozygous for the d allele, the A blood phenotype is not expressed, and those individuals are blood type B. [Side note: there is no such gene as gene D. This is a hypothetical question.] a. Describe the mode of inheritance of blood phenotypes in one or two sentences, using appropriate genetic terminology and accounting for both genes (I and D). b. What are the expected proportions (or ratios) of the four ABO blood phenotypes in the offspring if a double homozygous recessive O phenotype mother mates with a type A phenotype father who is homozygous for I but heterozygous for D? Show your work. c. What are the expected proportions (or ratios) of the four ABO blood phenotypes in the offspring if a double heterozygous A phenotype mother mates with a double heterozygous A phenotype father? Show your work.Explanation / Answer
a. The inheritance of blood group would follow the law of dominance. Gene D has two tyes of alleles dominant D and recessive d. Gene I has three types of alleles Ia, Ib and i. there are many possibilities which decides type of blood group in offspring. For example if Gene D is heterozygous and Gene I has Ia i genotype, then:
Dd (Gene D) x Ia i (Gene I)
Gametes
Ia
i
D
D Ia [Blood group A]
D i [Blood group A]
d
Ia d [Blood group A]
d i [Blood group --]
The type d i cannot specify which blood group will form because both alleles are recessive for individual blood group.
b. If mother has i i i i genotype for blood group O and father has blood group A (D d i i)
Gametes
D i
d i
i i
D i i i [Blood group A]
d i i i [Blood group O]
Gametes
Ia
i
D
D Ia [Blood group A]
D i [Blood group A]
d
Ia d [Blood group A]
d i [Blood group --]
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