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Practice - Co Dominance

Co-dominance occurs when two alleles of a gene express together, as seen in human blood groups controlled by alleles IA, IB, and IO. The document outlines the genotypes and phenotypes of blood groups A, B, AB, and O, and presents several genetic problems related to blood group inheritance. It also distinguishes between co-dominance and incomplete dominance, noting that in co-dominance, both alleles express equally.

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6 views3 pages

Practice - Co Dominance

Co-dominance occurs when two alleles of a gene express together, as seen in human blood groups controlled by alleles IA, IB, and IO. The document outlines the genotypes and phenotypes of blood groups A, B, AB, and O, and presents several genetic problems related to blood group inheritance. It also distinguishes between co-dominance and incomplete dominance, noting that in co-dominance, both alleles express equally.

Uploaded by

serahpanjwani
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© © All Rights Reserved
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Co Dominance:

Co dominance is a condition in which two alleles of a particular gene express together. Both have
their effect and is seen in the phenotype.

Example: Blood groups in humans

 Human blood groups are controlled by three alleles I A, IB, Io.(can be represented by AA, BB
and OO)
 IA is dominant over IO
 IB is dominant over IO
 IA and IB are co dominant
 The different genotypes of the blood groups are as follows:

Blood groups (phenotype) Genotypes


A IA IA (homozygous) or IA IO (heterozygous)

B IB IB (homozygous) or IB IO (heterozygous)

AB IA IB (codominant) always heterozygous

O IO IO always homozygous

Problems:

1. When a male with blood group A mates with a woman of blood group B, what will be the
phenotypes of the offspring, assuming that the male and female are heterozygous. What will
be their genotypes?
2. A man with a homozygous A blood group marries a woman with AB blood group. What are
the phenotypes and genotypes of F1?

3. A female with the blood group B married a male with blood group A. The offspring had the
blood group O also among them. What were the phenotypes and genotypes of the
offspring? What is the probability of the blood group O occurring?

4.
5.
6.
7.
8.
9.
10.
11.

A female with blood group O married a male with blood group B.

a. How is it possible for the couple to have a child with blood group O? What is the chance
of the couple having their first child with blood group B?
b. How is it possible for the couple to have all the children with the blood group B?

(please note: In co dominance expression of both the alleles will be 50% each.

In incomplete dominance which is a type of co dominance the percentage of expression of the


alleles can vary)

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