Name: Sex Determination (Drosophila melanogaster)
Uploaded: 2019-07-19
Duration: 7 min 20 s
Description: Drosophila melanogaster or the common fruit fly has contributed a lot to genetics. One of them is its sex determination system with more than five types of s...

Question

The pedigree diagram shows the known blood group in three generations of a family. Squares represent male and circle represent the females. What are the genotypes of 1 and 3? What is the blood group of 2?

Accepted Answer

The pedigree represents the biological relationships between an organism and its ancestors. The inheritance of the ABO blood group antigens in humans is an example of codominance. There are three alleles of the gene governing these characters instead of two, such as I^A, I^Band I^o. The alleles I^Aand I^Bare codominant, but both are dominant over I^o. In the given pedigree, in the 2^nd generation, one child has blood type O and it occurs in a condition in which both alleles are recessive (I^oI^o). It is possible only when both the parents are heterozygous.

In the given cross between blood type A and B, the male parent (1) has the genotype I^AI^o. In the 3^rd generation, one child having blood type AB that has the genotype I^AI^B, hence, the parents should be A or AB and B. So, the 2 represents blood type A or AB. If the 2 is blood type A, it should be heterozygous because the other child in 3^rd generation has blood type B. It is formed when a sperm with I^o is combined with an egg with I^B. Hence, the above pedigree diagram is completed as follows:

The genotype of 1 is I^AI^o.

The genotype of 2 is either I^AI^o(if the blood type is A) or I^AI^B(if the blood type is AB).

The pedigree diagram shows the known blood group in three generations of a family. Squares represent male and circle represent the females. What are the genotypes of 1 and 3? What is the blood group of 2?

Important Questions on Inheritance

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