60. The recessive allele that causes phenylketonuria (PKU) is harmful, except when an infant's diet lacks the amino acid, phenylalanine. What maintains the presence of this harmful allele in a population's gene pool?
(A) heterozygote advantage
(B) stabilizing selection
(C) diploidy
(D) balancing selection
(E) kin selection

56. Sequencing an entire genome, such as that of Caenorhabditis elegans, a nematode, is most important because (A) it allows researchers to use the sequence to build a "better" nematode, resistant to disease. (B) it allows research on a group of organisms we do not usually care much about. (C) the nematode is a good animal model for trying out cures for viral illness. (D) a sequence that is found to have a particular function in the nematode is likely to have a closely related function in vertebrates. (E) a sequence that is found to have no introns in the nematode genome is likely to have acquired the introns from higher organisms.

57. Countercurrent exchange in the fish gill helps to maximize which of the following? (A) endocytosis (B) blood pressure (C) diffusion (D) active transport (E) osmosis

58. Sexual reproduction (A) allows animals to conserve resources and reproduce only during optimal conditions. (B) can produce diverse phenotypes that may enhance survival of a population in a changing environment. (C) yields more numerous offspring more rapidly than is possible with asexual reproduction. (D) enables males and females to remain isolated from each other while rapidly colonizing habitats. (E) guarantees that both parents will provide care for each offspring.

59. Members of two different species possess a similar-looking structure that they use in a similar fashion to perform the same function. Which information would best help distinguish between an explanation based on homology versus one based on convergent evolution? (A) The two species live at great distance from each other. (B) The two species share many proteins in common, and the nucleotide sequences that code for these proteins are almost identical. (C) The sizes of the structures in adult members of both species are similar in size. (D) Both species are well adapted to their particular environments. E) Both species reproduce sexually.

61. Bagworm moth caterpillars feed on evergreens and carry a silken case or bag around with them in which they eventually pupate. Adult female bagworm moths are larval in appearance; they lack the wings and other structures of the adult male and instead retain the appearance of a caterpillar even though they are sexually mature and can lay eggs within the bag. This is a good example of (A) allometric growth. (B) paedomorphosis. (C) sympatric speciation. (D) adaptive radiation. (E) changes in homeotic genes.

62. Hypothetical mutation in a squirrel population produces organisms with eight legs rather than four. Further, these mutant squirrels survive, successfully invade new habitats, and eventually give rise to a new species. The initial event, giving rise to extra legs, would be a good example of (A) punctuated equilibrium. (B) species selection. (C) habitat selection. (D) changes in homeotic genes. (E) allometry.

63. Species that are not closely related and that do not share many anatomical similarities can still be placed together on the same phylogenetic tree by comparing their (A) plasmids. (B) chloroplast genomes. (C) mitochondrial genomes. (D) homologous genes that are poorly conserved. (E) homologous genes that are highly conserved.

64. Animal communication involves what type of sensory information? (A) visual (B) auditory (C) chemical (D) A and C only (E) A, B, and C

65. Which of the following statements about histone acetylation is WRONG? (A) Histone acetylation usually occurs within the tail region. (B) Histone acetylation decreases the positive charge of histones. (C) Histone acetylation reduces the histone-DNA affinity. (D) Histone acetylation promotes the 30-nm fiber formation. (E) Histone acetylation is usually associated with activation of gene expression.

66. Which of the following statements is true? (A) miRNAs are made from long dsRNAs, whereas siRNAs are made from large hairpin precursors. (B) miRNAs are made from large hairpin precursors, whereas siRNAs are made from long dsRNAs. (C) Both miRNAs and siRNAs are made from long dsRNAs. (D) Both miRNAs and siRNAs are made from large hairpin precursors. (E) none of the above