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.

46. In a cell dividing by meiosis, DNA is replicated__? (A) between meiosis I and again before meiosis II；(B) during prophase I；(C) before meiosis I；(D) during prophase II.

47. In meiosis, homologous chromosomes align next to one another during__? (A) prophase I；(B) prophase II；(C) metaphase I；(D) metaphase II.

48. If the heterozygous phenotype is intermediate between those of the two different homozygotes, this is called__? (A) incomplete dominance；(B) independent assortment；(C) polygenic；(D) codominance.

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.

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.

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

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.