Question

Which of the following conditions is a hybrid breakdown?
A) Failure of hybrid adults to produce functional gametes
B) Failure of fusion of ova and egg of two species
C) Failure of hybrid zygote to develop into an offspring
D) None of the above

Answer 1

Hint: When organisms of two different species reproduce through sexual reproduction, the resulting offspring is known as a hybrid, and the process is called hybridization. The hybrid organisms are not always fertile. However, even if they are fertile, their progeny may show less vigour or may not be viable.

Complete answer:
Option (A): Hybrid adults that fail to produce functional gametes is an example of hybrid sterility. A classic example of hybrid sterility is demonstrated by mules. Mules are hybrids between male donkeys and female horses. The mules are sterile animals who cannot produce viable gametes.
Option (B): Ova and egg are different names of gametes produced by females. An ova or egg is produced by the ovaries and are haploid in nature, that is they contain one set chromosome. The egg or ova fuses with sperms produced by males, generally of the same species, to result in the formation of diploid offspring.
Option (C):. A hybrid breakdown occurs when fertile hybrids fail to produce viable offspring. Mostly the hybrids can produce fertile ${F_1}$ offspring. However, the cross between the ${F_1}$ population shows reduced viability of the ${F_2}$ progeny. The progeny may be weak or die early during development. The hybrid breakdown mechanism is considered to be a post zygotic reproductive isolation mechanism. Hybrid breakdown is seen more in plants than in animals.

Option C is the correct answer.

Note: Hybridization is more common in plants than in animals. Animals of two different species cannot reproduce by sexual reproduction because of different size and location of genitalia. However, it is easier to carry out hybridization in plants. Plant breeders often carry out the process to get desirable and viable plant species. However, the hybrid progenies always cannot produce viable offspring. This failure of a hybrid zygote to develop into a viable offspring is called hybrid breakdown.