25. The genetic variations necessary for natural selection are usually harmful.

Question

25. The genetic variations necessary for natural selection are usually harmful. b. are controlled by the environment. c. result in mutations. d. can be caused by recombination during meiosis e. all of the above are true 26. One necessary element of the biological species concept is: a. homologous isolation. b. divergent isolation. c. convergent isolation. d. reproductive isolation. 27. Individuals organisms in a population: a. compete with other members of their species. b. differ in fitness from other members of their species. c. are adapted to their environment. d. are related by descent from a common ancestor. e. all of the above are true 28. The Northern elephant seal went through a severe population decline as a result of hunting in the late 1800s. The population has rebounded but is now homozygous for nearly every gene studied. This is an example of a. negative assortive mating b. migration mutation d. a bottleneck e. disruptive selection.

Explanation / Answer

Q: 25: e) all of the above are true.

Explanation: Natural selection involves genetic variations due to mutations, environmental factors and variations among individuals’ produces offspring which can survive in future generation due to some differing features.

26. d) reproductive isolation.

Explanation: Biologically species are those individuals which interbreed among themselves. They cannot breed with other group of individuals or species. So this group is also called as reproductively isolated species.

27. e) all of the above are true.

Explanation: Individual organism in a population like a "human being" (for example) faces competition with other humans. Every human being belong to same species or is a descendant from a common ancestor but differs in physical appearance like colour, height, weight, fitness, etc. and the behaviour of human beings also differ based on the location and the environmental factors surrounding them.

28. d) a bottleneck.

Explanation: A bottleneck in biological terms or genetic terms means a provisional or temporary reduction in the population thus reducing the number of individuals which leads to the loss of genetic variation in the rebounded or future population. Due to lesser variations in the genes, the rebounded population’s genes are almost similar or homozygous.

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