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Principles Of Inheritance And Variation

Question
CBSEENBI12001637
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How does the gene 'I' control ABO blood groups in humans? Write the effect the gene has on the structure of red blood cells.

Solution

In humans, the ABO blood groups are controlled by a gene called gene I. It has three alleles, namely IA, IB and i. Two of the three alleles IA and I B dominate over i. But IA and I B express themselves in each other’s presence and hence are co-dominant.

Showing the Genetic Basis of Blood Groups in Human Population is given as follows:

 

Allele from Parent 1

Allele from Parent 2

Genotype of offspring

Blood type of offspring

I A

I A

I A I A

A

I A

I B

I A I B

AB

I A

i

I A i

A

I B

I A

I A I B

AB

I B

I B

I B I B

B

I B

i

I B i

B

i

i

i i

O


These alleles help to determine the structure of the red blood cells. The plasma membrane of red blood cells has sugar polymers that protrude out from its surface and the kind of sugar is regulated by the gene 'I' of ABO blood group. The alleles IA and IB produce A and B types of sugar, while allele i does not produce any sugar. Thus when allele ‘IA and IA’ and ‘I A and i‘ are present together then the red blood cells have sugar A on the surface. When IB and I B or IA and i are present then sugar B is found on the surface. When IA and I B are present both A and B sugar are found on the cell surface. While blood group O does not bear any sugar.

Some More Questions From Principles of Inheritance and Variation Chapter

Write down Mendel’s dihybrid Phenotypic ratio 

Who were the rediscoverers of Mendelism ?

What are the real determinants of what an organism will become ?

What is the unique feature of F1 generation ?

What will be the genetic make up of an organism which suffers from sickle cell anaemia ?

What do the symbols square and circle in a pedigree chart indicate ?

Define heterogamy. Give an example.

How many chromosomes are found in human cells ?

Why is male Drosophila regarded as heterogametic ?

What term is used for the two chromatids resulting from the interchange of segments during crossing over ?

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