Question

Parthenogenesis is the development of a female egg into a new individual without the contribution of a male set of chromosomes.
In a hypothetical pond, two populations of fish are found; one reproduces through sexual reproduction, the other through parthenogenesis. Initially, the parthenogenetic fish are a larger population when the pond is first studied. However, researchers soon observe that the parthenogenetic fish are more frequent hosts for a new blood-borne parasite than the sexually reproducing fish. As a result, the sexually reproducing population increases and the parthenogenetic population decreases.
Which of the following best explains the reason for the shift in population numbers?

• A. Sexual reproduction increases genetic variation. Some individuals in the sexually reproducing population will be adapted to a change in environment, in this case, the addition of a new parasite. These individuals will survive and reproduce at a higher rate than those affected by the parasite.
• B. The asexual fish are more susceptible to the parasites because they are an all female population, and typically less aggressive. The sexually reproducing population is protected by aggressive adult males fighting off the invading parasites.
• C. The asexually reproducing fish are intentionally reducing their population density as a mechanism to slow the spread of the parasite.
• D. The sexually reproducing population can reproduce faster than the parthenogenesis population, allowing them to produce so much offspring that not all can be affected by the new parasite.

Answer 1

The correct option is A Sexual reproduction increases genetic variation. Some individuals in the sexually reproducing population will be adapted to a change in environment, in this case, the addition of a new parasite. These individuals will survive and reproduce at a higher rate than those affected by the parasite.

Parthenogenetic fish are produced by asexual reproduction. Hence, genetic variation does not takes place in them. Whereas fishes that are produced sexually increases genetic variation. Due to genetic variation, this population can adapt to changing environment. When the pond is infected by blood-borne parasite, parthenogenetic fish could not adapt to this changed environment. However, fishes produced sexually will adapt to it. Due to genetic variation, it will survive and reproduce at a higher rate.

Thus, the correct answer is 'Sexual reproduction increases genetic variation. Some individuals in the sexually reproducing population will be adapted to a change in environment, in this case, the addition of a new parasite. These individuals will survive and reproduce at a higher rate than those affected by the parasite.'