Q63. The graph on the right shows the proportion of snails from different clonal

Question

Q63. The graph on the right shows the proportion of snails from different clonal strains infected by a parasite. The first four bars are from four distinct and relatively common clonal strains. The fifth bar is an average infection rate for 40 rarer strains. Imagine one of the rare snail strains with a low infection rate actually reproduces sexually. What would you expect to happen over time? The sexual population will stay rare or go extinct because the asexually reproducing snails can reproduce more quickly. The sexual population will first grow, while it is relatively rare, but then shrink and likely go extinct after it becomes common, because once it is common it will be attacked by parasites more frequently The sexual population will grow until it is more common than all the clonal populations, because it can more quickly evolve new protection from parasites. Q64. Now say you repeated the experiment but added a drug that killed all the parasites. What would you expect to happen over time? The sexual population will stay rare or go extinct because the asexually reproducing snails can reproduce more quickly. The sexual population will first grow, while it is relatively rare, but then shrink and likely go extinct after it becomes common, because once it is common it will be attacked by parasites more frequently The sexual population will grow until it is more common than all the clonal populations, because it can more quickly evolve new protection from parasites.

Explanation / Answer

Snails can reproduce either sexually or by hermaphrodite nature (asexual mode). Here, the rare strain has less rate infection rate than the strains 22, 63, 12 and 19. Based on the principle of natural selection the selection of genotypes occurs and that would result in offspring with better reproductive capabilities. Natural selection always results in better survival of organism independent of its pathogenicity.

1)

So, the sexual population will first grow, while it is relatively rte, but then shrinks and likely go extinct after it becomes common because once it is common it will be attached by parasites more frequently. Thus, the correct option is (b).

2)

Medical treatment inhibits the process of natural selection in many of the cases. For example, continuous treatment of tuberculosis help to cure the disease completely as it does not offer time to bacteria to develop resistant genotype through natural selection. However, with the irregular treatment of bacteria, natural selection comes into scene, which results in the development of resistant strain.

So, the sexual population will grow until it’s more common than all populations, because it can more quickly evolve new protection from parasites. Thus, the correct option is (c).

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