Question:

Grain colour in wheat is determined by three pairs of polygenes. Following the cross AABBCC (dark colour) x aabbcc (light colour), in $F_2$ generation what proportion of the progeny is likely to resemble either parent?

Updated On: Jul 27, 2022
  • Half
  • Less than 5 percent
  • One third
  • None of these
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The Correct Option is B

Solution and Explanation

Polygene results in quantitative inheritance which is characterised by occurrence of intermediate forms between the parental type. In case of crossing between AABBCC (dark colour) and aabbcc (light colour) in $F _{2}$ generation seven phenotypes will obtain with ratio of $1: 6: 15: 20: 15: 6: 1$. The total number of progeny is $64$, out of which only two will be likely resemble with either parents. Hence, their proportion in $F _{2}$ generation would be $3.12$ i.e., less than $5 \%$.
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Concepts Used:

Non-Mendelian Genetics

The term - non-mendelian inheritance refers to any pattern of heredity in which features do not separate according to Mendel's laws. These principles describe how features linked with single genes on chromosomes in the nucleus are passed down through generations.

Types of Non-Mendelian Inheritance

Codominance Inheritance

It is a form of incomplete dominance in which both alleles for the same feature are expressed in the heterozygote at the same time. For example, the MN blood types of humans.

Incomplete Dominance

In a heterozygote, the dominant allele does not always completely cover the phenotypic expression of the recessive gene, resulting in an intermediate phenotype which is referred to as "incomplete dominance”.