15. What is a ribozyme?
(A)an RNA with enzymatic activity
(B)an enzyme that modifies ribosomal RNA
(C) an enzyme that uses RNA as a substrate
(D)an enzyme that synthesizes RNA during the transcription process
(E)an enzyme that synthesizes RNA primers during DNA replication

11. What was the most significant conclusion that Gregor Mendel drew from his experiments with pea plants? (A)There is considerable genetic variation in garden peas. (B)Recessive genes occur more frequently in the F1 generation than do dominant ones. (C) Traits are inherited in discrete units, and are not the results of "blending." (D)Genes are composed of DNA. (E)An organism that is homozygous for many recessive traits is at a disadvantage.

12. In certain plants, tall is dominant to short. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short? (A)0(B)1/2(C)1/4(D)1/6(E)1

13. If one nondisjunction event occurs in meiosis II during gametogenesis, what will be the result at the completion of meiosis? (A)All the 4 gametes will be diploid (2n). (B)2 of the 4 gametes will be 2n, and 2 will be n. (C) 2 of the 4 gametes will be n + 1, and 2 will be n - 1. (D)2 of the 4 gametes will be n + 1 and n – 1, and 2 will be n.

14. Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. This occurs because their cells are impaired in what way? (A)They cannot replicate DNA. (B)They cannot repair thymine dimers. (C) They cannot undergo mitosis. (D)They cannot exchange DNA with other cells. (E)They do not recombine homologous chromosomes during meiosis.

16. Alternative RNA splicing (A)is a mechanism for increasing the rate of transcription. (B)is a mechanism for increasing the rate of translation. (C) can allow the production of different proteins from a single pre-mRNA. (D)is due to the presence or absence of particular snRNPs.

17. Which of the following statements about microRNAs is false? (A)MicroRNAs are short RNA molecules. (B)MicroRNAs are formed by cleavage of hairpin loops in a larger precursor. (C) MicroRNAs have internal complementary base pairs, folding into cloverleaf patterns. (D)MicroRNAs silence the expression of specific mRNAs. (E)MicroRNAs are found in plants and animals.

18. Which of the following statements describes proto-oncogenes? (A)Their normal function is to suppress tumor growth. (B)They are introduced to a cell initially by retroviruses. (C) They are produced by somatic mutations induced by carcinogenic substances. (D)They often encode proteins that stimulate the cell cycle. (E)They are underexpressed in cancer cells.

19. Muscle cells differ from nerve cells mainly because they (A)contain different genes. (B)express different genes. (C) use different genetic codes. (D)have unique ribosomes. (E)have different chromosomes.

20. What are prions? (A)mobile segments of DNA (B)tiny molecules of RNA that infect plants (C) misfolded versions of normal brain protein (D)viruses that invade bacteria

21. The reason for using Taq polymerase for PCR is that (A)only minute amounts are needed for each cycle of PCR. (B)it binds more readily than other polymerases to primer. (C) it is heat stable and can withstand the high temperature of PCR. (D)it can use RNA as template to synthesize DNA.