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

51. sexual reproduction and sexual reproduction are different in that (A) individuals reproducing asexually transmit 100% of their genes to their progeny, whereas individuals reproducing sexually only transmit 50%. (B) asexual reproduction produces offspring that are genetically identical to the parents, whereas sexual reproduction gives rise to genetically distinct offspring. (C) asexual reproduction involves a single parent, whereas sexual reproduction involves two. (D) asexual reproduction only requires mitosis, whereas exual reproduction always involves meiosis. (E) all of the above

52. Referring to a plant sexual life cycle, which of the following terms describes the process that leads directly to the formation of gametes? (A) sporophyte meiosis (B) gametophyte mitosis (C) gametophyte meiosis (D) sporophyte mitosis (E) alternation of generations

53. The F1 offspring of Mendel's classic pea cross always looked like one of the two parental varieties because (A) one allele was completely dominant over another. (B) each allele affected phenotypic expression. (C) the traits blended together during fertilization. (D) no genes interacted to produce the parental phenotype. (E) different genes interacted to produce the parental phenotype.

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.

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

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

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.