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Question
How many of the following statements are correct?
Statement I: Recombination of genes is directly proportional to the strength of linkage.
Statement II: Recombination of genes is inversely proportional to the strength of linkage.
Statement III: More the distance between the two genes on a chromosome, less the strength of linkage.
Statement IV: More the distance between the two genes on a chromosome, more the strength of linkage.
Statement V: Recombination frequency is inversely proportional to the distance between the genes present on a chromosome.
How many of the following statements are correct?
Statement I: Recombination of genes is directly proportional to the strength of linkage.
Statement II: Recombination of genes is inversely proportional to the strength of linkage.
Statement III: More the distance between the two genes on a chromosome, less the strength of linkage.
Statement IV: More the distance between the two genes on a chromosome, more the strength of linkage.
Statement V: Recombination frequency is inversely proportional to the distance between the genes present on a chromosome.
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Solution
The correct option is C Two
Statements II and III are correct.
Statements I, IV and V are incorrect.
Linkage is the phenomenon of physical association of the genes on a chromosome which have the tendency to stay close together and get inherited together as a unit without separation. These genes can, however, get separated from each other instead of getting inherited as a unit, by an event called crossing over. Crossing over is the process of exchange of segments of non-sister chromatids of homologous chromosomes, that occurs at the pachytene stage of meiosis during gamete formation. This leads to the generation of new combinations of genes and the process is called recombination. After recombination these genes are then inherited together.
If genes are placed very close to each other on the same chromosome, chances of crossing over is very low. This lowers the chances of recombination. Hence, the strength of linkage would be more.
If the distance between genes on the same chromosome is more, chances of crossing over between them is high. This increases the chances of recombination. Hence, the strength of linkage would be less.
Conclusion:
1. Lesser the strength of linkage, greater is the chance of recombination.
2. Therefore, recombination is inversely proportional to the strength of linkage.
3. Greater the distance between two genes, lesser is the strength of linkage and higher is the chance of recombination.
4. Therefore,more the distance between the genes on the chromosome,more is the recombination frequency.
5. Recombination frequency is directly proportional to the distance between the genes, while linkage is inversely proportional to it.
Statements II and III are correct.
Statements I, IV and V are incorrect.
Linkage is the phenomenon of physical association of the genes on a chromosome which have the tendency to stay close together and get inherited together as a unit without separation. These genes can, however, get separated from each other instead of getting inherited as a unit, by an event called crossing over. Crossing over is the process of exchange of segments of non-sister chromatids of homologous chromosomes, that occurs at the pachytene stage of meiosis during gamete formation. This leads to the generation of new combinations of genes and the process is called recombination. After recombination these genes are then inherited together.
If genes are placed very close to each other on the same chromosome, chances of crossing over is very low. This lowers the chances of recombination. Hence, the strength of linkage would be more.
If the distance between genes on the same chromosome is more, chances of crossing over between them is high. This increases the chances of recombination. Hence, the strength of linkage would be less.
Conclusion:
1. Lesser the strength of linkage, greater is the chance of recombination.
2. Therefore, recombination is inversely proportional to the strength of linkage.
3. Greater the distance between two genes, lesser is the strength of linkage and higher is the chance of recombination.
4. Therefore,more the distance between the genes on the chromosome,more is the recombination frequency.
5. Recombination frequency is directly proportional to the distance between the genes, while linkage is inversely proportional to it.
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