64. Why do histones bind tightly to DNA?
(A) Histones are positively charged, and DNA is negatively charged.
(B) Histones are negatively charged, and DNA is positively charged.
(C) Both histones and DNA are strongly hydrophobic.
(D) Histones are covalently linked to the DNA.
(E) Histones are highly hydrophobic, and DNA is hydrophilic.

60. If A, B, and C are all required for growth, a strain mutant for the gene encoding enzyme B would be capable of growing on which of the following media? (A) minimal medium (B) minimal medium supplemented with "A" (C) minimal medium supplemented with "B" (D) minimal medium supplemented with "C" (E) answers B and C

61. Viruses are referred to as obligate parasites because (A) they cannot reproduce outside of a host cell. (B) viral DNA always inserts itself into host DNA. (C) they invariably kill any cell they infect. (D) they can incorporate nucleic acids from other viruses. (E) they must use enzymes encoded by the virus itself.

62. Which of the following statements about the lysogenic cycle of lambda (λ) phage is incorrect? (A) After infection the viral genes immediately turn the host cell into a lambda-producing factory, and the host cell then lyses. (B) Most of the prophage genes are silenced by the product of a particular prophage gene. (C) The phage genome replicates along with the host genome. (D) Certain environmental triggers can cause the phage to exit the host genome, switching from the lysogenic to the lytic cycle. (E) The phage DNA is incorporated by genetic recombination (crossing over) into a specific site on the host cell's DNA.

63. Which of the following statements concerning the eukaryotic chromosome is false? (A) It is composed of DNA and protein. (B) The nucleosome is the most basic structural subunit. (C) The number of genes on each chromosome is different in different cell types. (D) It consists of a single linear molecule of double-stranded DNA. (E) Active transcription occurs on euchromatin.

65. What is the enzymatic function of restriction enzymes? (A) to add new nucleotides to the growing strand of DNA (B) to join nucleotides during replication (C) to join nucleotides during transcription (D) to cleave nucleic acids at specific sites (E) to repair breaks in sugar-phosphate backbones

66. Bacteria containing recombinant plasmids are often identified by which process? (A) examining the cells with an electron microscope (B) using radioactive tracers to locate the plasmids (C) exposing the bacteria to an antibiotic that kills cells lacking the plasmid (D) removing the DNA of all cells in a culture to see which cells have plasmids (E) producing antibodies specific for each bacterium containing a recombinant plasmid.

67. A eukaryotic protein can be made in bacteria by inserting the gene encoding the protein into a(n) (A) protein plasmid. (B) expression vector. (C) yeast artificial chromosome (YAC). (D) PCR vector. (E) restriction plasmid.

68. One striking difference between development in plants and development in animals is the importance of cell in animal embryos. (A) division (B) differentiation (C) growth (D) movement (E) death

69. A cell that remains entirely flexible in its developmental possibilities is said to be (A) differentiated. (B) determined. (C) totipotent. (D) genomically equivalent. (E) epigenetic.

70. Catastrophism, meaning the regular occurrence of geological or meteorological disturbances (catastrophes), was Cuvier's attempt to explain the existence of (A) evolution. (B) the fossil record. (C) uniformitarianism. (D) the origin of new species. (E) natural selection.