53. Natural selection acts on__?
(A) genotypes；
(B) populations；
(C) individuals；
(D) communities.

49. Linked genes, by definition, are genes that__? (A) have no alleles；(B) have more alleles than usual；(C) are alleles that are found in different daughter cells；(D) are found on the same chromosome.

50. A single chromosome has__? (A) a single gene with multiple alleles；(B) a single gene with a single allele；(C) multiple genes, each with multiple alleles；(D) multiple genes, each with a single allele.

51. The method used to produce the cloned sheep, Dolly, was__? (A) embryonic stem cell transplantation；(B) polymerase chain reaction；(C) short tandem repeats；(D) somatic cell nuclear transfer.

52. Darwin concluded from his observations of nature and readings that__? (A) population growth is unlimited, leading to the large numbers of organisms；(B) individuals compete with one another for limited resources and only the fittest survive；(C) an individual's likelihood of survival and reproduction are mostly due to chance and changes in the environment；(D) individuals compete with one another for limited resources and only the fittest reproduce.

54. If similarities between two structures in different organisms reflect independent evolution, these structures are__? (A) heterologous；(B) homeotic；(C) homologous；(D) analogous.

55. The observation that most aquatic vertebrates (e.g. fish, penguins, and whales) have streamlined bodies and fins or flippers for steering are a result of__? (A) analogous selection；(B) convergent evolution；(C) sexual selection；(D) vestigial selection.

56. The enzyme that HIV uses to copy its RNA into DNA is__? (A) Reverse transcriptase；(B) RNA polymerase；(C) RNA integrase；(D) DNA polymerase.

57. A vaccine against the influenza virus would result in production of antibodies against which of the following? (A) proteins in the envelope；(B) lipids in the envelope；(C) viral DNA；(D) viral RNA.

58. Viruses always lack which of the following? (A)an envelope；(B) organelles；(C) genetic material；(D) a protein coat.

59. A microbiologist Gram stains a bacterium and finds the bacterium to be pink to red in color, this identifies the__? (A) species of bacterium；(B) bacterium as a bacterium that causes human disease；(C) bacterium as gram-negative；(D) bacterium as gram-positive.