Question

Which of the following shows a linkage group in the coupling phase?

Answer 1

Linkage is the close association of genes or the DNA sequences on the same chromosome. The genes that are presently closer to each other have high chances to be inherited together. It reduces the chance of recombination in genes.

Complete answer:
Two genetic markers that are physically near to each other and are unlikely to be separated onto different chromatids during chromosomal crossover are said to be more linked than markers that are far apart. In other words, the nearer two genes are on a chromosome, the lower the chance of recombination between them, and thus the more likely they are to be inherited together. Markers on different chromosomes are perfectly unlinked and have chances of recombination. The genes of hair colour and eye colour are linked. Therefore, in many cases, they are inherited together like blonde hair is linked with blue eyes, brown hair with brown eyes as so on.

The coupling phase is the phase when the two genes inherit together and it causes variability. In the figure, the two genes A and B are located on the same gene and are inherited together and thus shows linkage in the coupling phase. In figure, b, c, d the allele of the genes are located on the same chromosome therefore it does not show linkage.

Thus, the correct answer is option A.

Note: A linkage map (also called as a genetic map) is a table for a species/experimental population that shows the position of its known genes or genetic markers relative to each other. It is based on the recombination frequency, rather than a specific physical distance along each chromosome.