- In a plant species, a segregating line (one that contains both homozygotes and heterozygotes at a locus) can be made homozygous by repeated selfing for several
generations. What is the level of remaining heterozygosity after three generations of selfing, if
the level of heterozygosity in generation ‘O’ is denoted as 1?
(1) 0.5 (2) 0.25
(3) 0.125 (4) 0.0625The Principle: Heterozygosity Halves Each Generation
With each generation of selfing, the level of heterozygosity is reduced by half. If we denote the initial heterozygosity (generation 0) as 1, then after each generation, the remaining heterozygosity is:
Hn=(12)n
where n is the number of generations of selfing.
Step-by-Step Calculation
-
Generation 0 (starting point):
Heterozygosity = 1 -
Generation 1:
Heterozygosity = 12 = 0.5 -
Generation 2:
Heterozygosity = 12×0.5=0.25 -
Generation 3:
Heterozygosity = 12×0.25=0.125
So, after three generations of selfing, the remaining heterozygosity is 0.125 of the original level.
Why This Happens
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Selfing increases homozygosity: Each generation, half of the heterozygotes become homozygotes, rapidly reducing genetic diversity.
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Pure lines: This process is used in plant breeding to create genetically uniform lines.
Match with Provided Options
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(1) 0.5
-
(2) 0.25
-
(3) 0.125
-
(4) 0.0625
The correct answer is (3) 0.125.
Conclusion
After three generations of selfing, only 12.5% of the original heterozygosity remains in a segregating plant line. This rapid decline highlights the power of selfing to create homozygous lines in plant breeding programs.
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