Goats and sheep belong to the same family but different genera. While they often live together in the same pastures, the hybrid offspring that are occasionally produced between the two species rarely survive. When such a hybrid does survive, it is usually sterile. Which of the following best explains the mechanism that maintains reproductive isolation between goats and sheep? a. Gene flow is prevented because the two species belong to different trophic levels and therefore do not share a food source.
b. Habitat isolation creates a prezygotic barrier between the two species.
c. The males of one species and the females of the other species are fertile at different times.
d. The two species have a different number of chromosomes, resulting in a postzygotic barrier.

d. The two species have a different number of chromosomes, resulting in a postzygotic barrier.

Explanation:

The two species i.e. sheep and goat have different number of chromosomes that resulting in a postzygotic barrier. Sheep has 56 number of chromosomes whereas goat has 60 number of chromosomes that causes postzygotic barrier in the offspring produced from the fusion of these two species. Postzygotic barrier leads to the creation of a hybrid that is sterile and unable to produce offspring because of difference in chromosome number.

dz nuts.   eeneneneeenenne

answer: land bridge theory. land bridge theory held that shifting portions of dry land explained the finding of identical species on different continents. plate tectonic theory eventually eliminated the land bridge theory.