20. A laboratory might use dideoxyribonucleotides to  ________.
(A) separate DNA fragments
(B) produce cDNA from mRNA
(C) sequence a DNA fragment
(D) visualize DNA expression

16. What is the role of DNA ligase in the elongation of the lagging strand during DNA replication? (A) It synthesizes RNA nucleotides to make a primer. (B) It joins Okazaki fragments together. (C) It unwinds the parental double helix. (D) It stabilizes the unwound parental DNA.

17. An original section of DNA has the base sequence AGCGTTACCGT. A mutation in this DNA strand results in the base sequence AGGCGTTACCGT. This change represents  ________.(A) a missense mutation (B) a point mutation (C) a silent mutation (D) frameshift mutation

18. Imagine that you've isolated a yeast mutant that contains histones resistant to acetylation. What phenotype do you predict for this mutant? (A) The mutant will grow rapidly. (B) The mutant will require galactose for growth. (C) The mutant will show low levels of gene expression. (D) The mutant will show high levels of gene expression.

19. Which of the following human diseases is caused by a virus that requires reverse transcriptase to transcribe its genome inside the host cell? (A) herpes (B) AIDS (C) smallpox (D) influenza

21. When gene duplication occurs to its ultimate extent by doubling all genes in a genome, what has occurred? (A) pseudogene creation (B) creation of a gene cluster (C) creation of a polyploid (D) creation of a diploid

22. A farmer uses triazine herbicide to control pigweed in his field. For the first few years, the triazine works well and almost all the pigweed dies； but after several years, the farmer sees more and more pigweed. Which of these explanations best explains what happened? (A) The herbicide company lost its triazine formula and started selling poor-quality triazine. (B) Natural selection caused the pigweed to mutate, creating a new triazine-resistant species. (C) Triazine-resistant pigweed has less-efficient photosynthesis metabolism. (D) Triazine-resistant weeds were more likely to survive and reproduce.

23. Mutation is the only evolutionary mechanism that  ________.(A) does little to change allele frequencies (B) is more important in eukaryotes than in prokaryotes (C) happens in all populations (D) has no effect on genetic variation

24. Plant species A has a diploid number of 12. Plant species B has a diploid number of 16. A new species, C, arises as an allopolyploid from A and B. The diploid number for species C would probably be  ________.(A) 14 (B) 16 (C) 28 (D) 56

25. If one organ is an exaptation of another organ, then these two organs  ________.(A) are homologous (B) are undergoing convergent evolution (C) are found in the same species (D) have the same function

26. Phylogenetic trees constructed from evidence from molecular systematics are based on similarities in  ________.    (A) morphology (B) the pattern of embryological development (C) biochemical pathways (D) mutations to homologous genes