16. Excision repair corrects DNA by
(A) detecting, removing, and replacing damaged or incorrect nucleotides in a single strand of DNA.
(B) excising the incorrect base from a nucleotide.
(C) removing extraneous groups such as methyl or oxygen added by mutagens.
(D) correcting A=T to C-G transitions.

12. In order to express eukaryotic genes in a bacterium, the _____ must first be removed. (A) introns (B) exons (C) enhancers (D) 3' poly （Ａ） sequence

13. What is one statement that would support the theory that all organisms are related? (A) The genetic code is almost universal. (B) Eukaryotes have mitochondria. (C) All organisms have nuclei. (D) Prokaryotes have circular chromosomes.

14. Which one of the following is not an element found in DNA? (A) Oxygen. (B) Sulfer. (C) Nitrogen. (D) Phosphate.

15. The heritable disorder Fragile X syndrome, a major cause of mental retardation, is caused by (A) production of enzymes that break the phosphate backbone. (B) X-ray. (C) presence of an extra chromosome in the sperm or egg. (D) duplication of multiple three-nucleotide repeats.

17. Histones and DNA have a strong attraction for each other because (A) DNA is positively charged and histones are negatively charged. (B) both DNA and proteins are hydrophobic. (C) DNA is negatively charged and histones are positively charged. (D) like substances share common charges.

18. Which one of the following is   NOT   a cis-regulatory element in gene transcription (A) bHLH-type protein. (B) promoter. (C) enhancer. (D) insulator.

19. In order to perform polymerase chain reactions (PCR), which of the following components is required? (A) DNA ligase. (B) Sense and antisense DNA primers encompassing the DNA region of interest. (C) A vector with a selectable marker. (D) An origin of replication specific for the bacterium Thermophilus aquaticus.

20. The Nobel Prize in Physiology or Medicine 2019 was awarded for the discovery of what? (A) Cancer therapy by inhibition of negative immune regulation. (B) How cells sense and adapt to oxygen availability. (C) Mechanisms for autophagy. (D) Molecular mechanisms controlling circadian rhythm.

21. What is   NOT   true about Sanger sequencing? (A) It was developed by Frederick Sanger and colleagues in 1977. (B) The most widely used sequencing method for approximately 40 years. (C) A method based on in vitro DNA digestion. (D) Incorporation of chain-terminating dideoxynucleotides.

22. What is an "Okazaki fragment"? (A) The strand of nascent DNA which is synthesized in the same direction as the growing replication fork. (B) A short single-stranded nucleic acid utilized by all living organisms in the initiation of DNA synthesis. (C) Short sequences of DNA nucleotides which are synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication. (D) A particular sequence in a genome at which replication is initiated.