Frequency of recombination between two genes is affected by-
A. Coupling and repulsion phase of linkage
B. Asynapsis and desynapsis
C. Location of the gene with respect to the centromere
D. Distance between two genes
E. Translocation of the genes
Choose the correct answer from the options given below:
A. Coupling and repulsion phase of linkage
B. Asynapsis and desynapsis
C. Location of the gene with respect to the centromere
D. Distance between two genes
E. Translocation of the genes
Choose the correct answer from the options given below:
Show Hint
The phase (AB/ab or Ab/aB) tells you what you will get.
The frequency ($r$) tells you how much you will get.
The "how much" depends on the physical architecture (distance, centromere) and the process (synapsis).
- A, B, C and D only
- A, C, D and E only
- B, C, D and E only
- A, B, C and E only
The Correct Option is C
Solution and Explanation
Recombination frequency ($r$) is the percentage of recombinant offspring produced. It is used to measure the genetic distance between loci on a chromosome.
Step 2: Detailed Explanation:
• Distance between genes (D): This is the primary factor. According to Sturtevant’s principle, the probability of a crossover occurring between two points increases as the physical distance between them increases.
• Centromere Location (C): Recombination is not uniform across a chromosome. Crossovers are generally suppressed in regions near the centromere (the "centromere effect"). Thus, two genes near a centromere will show lower recombination than two genes at the same physical distance in a more distal region.
• Asynapsis and Desynapsis (B): These are genetic or environmental conditions where homologous chromosomes fail to pair properly (asynapsis) or separate prematurely (desynapsis) during meiosis. Without proper pairing, crossing over cannot occur, drastically reducing recombination frequency.
• Translocation (E): Large-scale chromosomal rearrangements like translocations can move genes to different linkage groups or to regions where recombination rates are different (e.g., closer to a centromere or telomere), thus altering their observed recombination frequency.
• Coupling vs. Repulsion (A): These refer to the phase of linkage (AB/ab vs. Ab/aB). While the phase determines which gametes are recombinant, it does not change the frequency ($r$) of recombination itself. The value of $r$ for a given distance remains constant regardless of whether the alleles are in coupling or repulsion.
Final Answer:
Recombination frequency is affected by B, C, D, and E. It is independent of the phase (A).
The correct combination is B, C, D, and E only.
The corresponding option is (C).
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