Question

How many linkage groups are present in human males?
24
23
46
22

Answer 1

Hint: A set of genes that remain together during meiosis or inheritance form a linkage group.

Complete answer:
1. A chromosome constitutes one linkage group. The maximum number of linkage groups is generally equal to the haploid chromosome number of an organism.
2. For example, there are 4 linkage groups in Drosophila melanogaster (2n=8), 7 in garden pea (2n=14), etc.
3. But the linkage group corresponds to the total number of different chromosomes of that species, and not simply a haploid or diploid number.
4. So, exceptionally, human males have 24 linkage groups (46, XY), that is 22 autosomes, and an 'X' and a 'Y' chromosome.

Additional Information:
1. The phenomenon of 'Linkage' was first reported by 'Bateson' and 'Punnet' in 1906.
2. T. H. Morgan studied linkage in Drosophila melanogaster in detail and concluded that linkage occurs by 'repulsion' and 'coupling'.
3. The linkage groups (linked genes on chromosome) do not segregate at the time of division
4. It reduces variability.
5. The more closely genes located, the more is the linkage.
6. The linkage between two desirable genes is advantageous for the plant breeder.

So, the correct answer is ‘24’.

Note:
1. Linkage groups in a human female are 23 (22 autosomes and an X chromosome).
2. Linkage differs from crossing over as the latter involves the exchange of genetic material between non-sister chromatids of the homologous chromosome.
3. If the dominant allele pairs with another dominant allele during linkage, it is known as the Coupling phase.
4. If the dominant allele links with a recessive allele on the same chromosome during linkage, it is known as the repulsive phase.