The type of reproductive barrier that occurs when two species mate but produce sterile hybrids is referred to as
a. mechanical isolation
b. temporal isolation
c. a post-zygotic barrier
d. behavioral isolation
The correct answer and explanation is :
The correct answer is c. a post-zygotic barrier.
Explanation:
A post-zygotic barrier refers to a reproductive barrier that occurs after fertilization, preventing the successful reproduction of viable offspring. One specific example of a post-zygotic barrier is when two species mate and produce hybrids, but these hybrids are sterile. This phenomenon is best exemplified by the mule, which is a sterile hybrid resulting from the mating of a male donkey and a female horse. While the mule is a hybrid, it cannot reproduce due to its sterility, which is a result of genetic incompatibility between the two parent species.
Post-zygotic barriers are mechanisms that operate after the sperm fertilizes the egg, and they prevent successful reproduction even if fertilization occurs. Sterility of hybrids is a direct consequence of genetic differences between the parent species that lead to issues such as problems during meiosis or chromosomal incompatibility in the offspring. These barriers are crucial in maintaining reproductive isolation between species and ensuring that distinct species do not blend into one another.
To contrast, pre-zygotic barriers prevent mating or fertilization from happening at all. These include:
- Mechanical isolation (a): Physical differences between species that prevent mating, such as the size and shape of reproductive organs.
- Temporal isolation (b): Species may mate at different times (e.g., different seasons or times of day), preventing interbreeding.
- Behavioral isolation (d): Differences in mating behaviors (like courtship rituals) prevent species from mating.
In the case of post-zygotic barriers, the hybrid may be produced initially, but it lacks the ability to reproduce, thereby preventing gene flow between the species. This ensures that the species maintain their genetic distinctiveness over time, despite the possibility of interbreeding.