10. After meiosis the 20 % gametes are recombinant for two genes. The distance between two genes will be
(1) 5 Cm (2) 10 cM
(3) 20 cM (4) 40 CM
The distance between two genes is directly proportional to the percentage of recombinant gametes formed after meiosis. If 20% of the gametes are recombinant for two genes, the distance between these genes is 20 centiMorgans (cM).
Explanation of the Answer
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Recombination frequency is the percentage of recombinant gametes produced due to crossing over between two genes during meiosis.
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This frequency is expressed as a percentage and is equivalent to the genetic distance in centiMorgans (cM).
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Therefore, if the recombination frequency is 20%, the distance between the two genes is 20 cM.
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This means 20% of the gametes are recombinant, reflecting a 20 cM map distance between the genes on the chromosome.
Explanation of Each Option
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5 cM: A 5 cM distance indicates a 5% recombination frequency. Since the question states 20% recombinant gametes, 5 cM is too small.
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10 cM: A 10 cM distance corresponds to 10% recombination frequency, which is half of the given 20%. This is incorrect.
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20 cM: This matches the 20% recombinant gametes, so the genes are 20 cM apart. This is the correct answer.
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40 cM: A 40 cM distance means 40% recombination frequency, double the observed 20%, so this is incorrect.
Introduction
The genetic distance between two genes during meiosis can be estimated by calculating the percentage of recombinant gametes produced. This is a fundamental concept in genetics used for gene mapping and understanding genetic linkage. In this article, we explain how to determine gene distance with a focus on recombinant gamete percentages like 20%, and clarify common confusions with detailed examples.
This genetic concept states that the recombination frequency is equal to the map distance between genes, where 1% recombination corresponds to 1 centiMorgan (cM). Thus, a 20% recombination frequency means a 20 cM distance between genes, clearly explaining the problem in this question. The correct choice out of the options provided is 20 cM.
This principle is a core part of classical genetics and helps in constructing gene linkage maps used in genetics research and breeding programs.
