21. The elongation of the leading strand during DNA synthesis
(A)depends on the action of DNA polymerase.
(B)occurs in the 3’→5’direction.
(C)produces Okazaki fragments.
(D)progresses away from the replication fork.
(E)dependents on the activity of helicase

17. In tigers, a recessive allele of a particular gene causes both an absence of fur pigmentation (a white tiger) and a cross‐eyed condition. If two phenotypically normal tigers that are heterozygous at this locus are mated, what percentage of their offspring will be cross‐eyed? (A)100% (B)10% (C)25% (D)50% (E)75%

18. Which of the following do you expect if an individual is heterozygous for the sickle‐cell trait? (A)they will not develop sickle‐cell disease (B)they will show some symptoms of the disease because the allele that causes sickle‐cell disease is not really recessive (C)they will be more apt to acquire a serious case of malaria (D)they will have full‐blown sickle‐cell disease because the allele is dominant (E)none of the listed choices are correct

19. Hemochromatosis is an inherited disease caused by a recessive allele. If a woman and her husband, who are both carriers, have three children, what is the probability of all three children have the disease? (A)3/4 (B)1/64 (C)37/64 (D)27/64 (E)7/64

20. In his work with pneumonia‐causing bacteria and mice, Griffith found that ______(A)the protein coat from pathogenic cells was able to transform nonpathogenic cells. (B)some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic. (C)the polysaccharide coat of bacteria caused pneumonia. (D)heat‐killed pathogenic cells caused pneumonia. (E)the third and fourth answers are correct.

22. The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage? (A)telomerase, primase, DNA polymerase (B)telomerase, helicase, single‐strand binding protein (C)nuclease, DNA polymerase, DNA ligase (D)DNA ligase, replication fork proteins, adenylyl cyclase (E)helicase, RNA primer, Okazaki fragments

23. Which of the following is true of a codon? (A)It never codes for the same amino acid as another codon. (B)It can be either in DNA or in RNA. (C)It is the basic unit of protein structure. (D)It can code for more than one amino acid. (E)Multiple codons can form complexes

24. In eukaryotic cells, transcription cannot begin until _______(A)the DNA introns are removed from the template. (B)the two DNA strands have completely separated and exposed the promoter. (C)several transcription factors have bound to the promoter. (D)the 5’ caps are removed from the mRNA. (E)the mitosis of cell division

25. Which of the following tools of DNA technology is incorrectly paired with its use? (A)reverse transcriptase−producƟon of cDNA from mRNA (B)DNA ligase−cuƫng DNA, creaƟng sƟcky ends of restricƟon fragments (C)electrophoresis−separaƟon of DNA fragments (D)DNA polymerase−polymerase chain reacƟon to amplify secƟons of DNA (E)RestricƟon enzyme−digest DNA molecules with specific sequence features

26. Animals that possess homologous structures probably __________. (A)have increased genetic diversity (B)are not related (C)are headed for extinction (D)had similar mutations in the past by chance (E)evolved from the same ancestor

27. By definition, a clade is __________. (A)parsimonious (B)polyphyletic (C)monophyletic (D)paraphyletic (E)analogous