Inbreeding is carried out in animal husbandry because it:

The correct answer is Option (4) → Increase homozygosity

Inbreeding is the mating of more closely related individuals within the same breed for 4–6 generations.

Option (1) Increase hybrid vigour — Incorrect. Hybrid vigour comes from crossing unrelated breeds. Continued inbreeding in fact lowers fertility and productivity (inbreeding depression).

Option (2) Improves the breed — Incorrect. Inbreeding helps fix good genes, but its direct result, the reason it is carried out, is pure lines through homozygosity.

Option (3) Increase heterozygosity — Incorrect. Inbreeding mates closely related animals, which brings like alleles together. NCERT says it increases homozygosity; heterozygosity is raised by out-breeding instead.

Option (4) Increase homozygosity — Correct. Inbreeding is the mating of more closely related individuals of the same breed for 4-6 generations. It increases homozygosity, so it is needed to evolve a pure line in any animal; it also exposes harmful recessive genes, which can then be removed.

Note: This question is from Chapter 9, Strategies for Enhancement in Food Production, of the pre-rationalised NCERT book. This chapter is not in the present NCERT book (2026-27). The extract below is from the pre-rationalised edition.

NCERT Extract (Pre-rationalised edition, Chapter 9, Strategies for Enhancement in Food Production):
Animal Breeding – “… Try to recollect the homozygous purelines developed by Mendel as discussed in Chapter 5. A similar strategy is used for developing purelines in cattle as was used in case of peas. Inbreeding increases homozygosity. Thus inbreeding is necessary if we want to evolve a pureline in any animal. Inbreeding exposes harmful recessive genes that are eliminated by selection.”