58. In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?
(A) DNA does not contain sulfur, whereas protein does.
(B) DNA contains phosphorus, but protein does not.
(C) DNA contains nitrogen, whereas protein does not.
(D) A and B only
(E) A, B, and C

54. Two plants are crossed, resulting in offspring with a 3:1 ratio for a particular trait. This suggests (A) that the parents were true-breeding for contrasting traits. (B) incomplete dominance. (C) that a blending of traits has occurred. (D) that the parents were both heterozygous. (E) that each offspring has the same alleles.

55. New combinations of linked genes are due to which of the following? (A) nondisjunction (B) crossing over (C) independent assortment (D) mixing of sperm and egg (E) both A and C

56. Which of the following statements is (are) true? (A) The closer two genes are on a chromosome, the higher the probability that a crossover will occur between them. (B) The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 50%. (C) Two of the traits that Mendel studied-seed color and flower color-are linked on the same chromosome. (D) Only B and C are correct. (E) A, B, and C are correct.

57. What does transformation involve in bacteria? (A) the creation of a strand of DNA from an RNA molecule (B) the creation of a strand of RNA from a DNA molecule (C) the infection of cells by a phage DNA molecule (D) the type of semiconservative replication shown by DNA (E) assimilation of external DNA into a cell

59. A mutation results in a defective enzyme A. Which of the following would be a consequence of that mutation? (A) an accumulation of A and no production of B and C (B) an accumulation of A and B and no production of C (C) an accumulation of B and no production of A and C (D) an accumulation of B and C and no production of A (E) an accumulation of C and no production of A and B

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.

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.