1. In humans, the genetic basis for determining the sex male is accomplished by

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1 BIOL. 303 EXAM II 10/26/ This exam consists of 40 multiple choice questions worth 2.5 points each. On the separate answer sheet, please fill-in the single best choice for each question. Please bubble-in your name on the answer sheet, leaving a space between first and last names. Also, bubble-in the last 5 digits of your social security number under ID NUMBER beginning in the left-most column. Good luck! In humans, the genetic basis for determining the sex male is accomplished by A. the Y chromosome B. the presence of only one X chromosome C. a balance between the number of X chromosomes and the number of haploid sets of autosomes D. multiple alleles scattered throughout the autosomes 2. Klinefelter syndrome in humans, which leads to underdeveloped testes and sterility, is caused by which chromosomal condition? A. 47, XXY B. 47, 21+ C. 45, X D. 47, XYY 3. In birds, sex is determined by a ZW chromosome scheme, which is much like the typical XY scheme seen in humans and many other organisms. However, in birds the system is reversed. Males are ZZ (similar to XX in humans) and females are ZW (similar to XY in humans). A lethal recessive allele that causes death of the embryo occurs on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male heterozygous for the lethal allele and a normal female? A. 2:1 male to female B. 3:1 male to female C. 1:2 male to female D. 1:1 male to female 4. Hemophilia is caused by a sex-linked recessive gene. Assume that a man with hemophilia marries a normal woman whose father had hemophilia. What is the probability that their first born child has hemophilia? A. 1/16 B. 1/8 C. 1/4 D. 1/2

2 5. A Barr body is A. a gene on the X chromosome that is responsible for female development. B. a patch of cells that has a phenotype different from surrounding cells because of variable X inactivation. C. an inactivated Y chromosome, visible in the nucleus of a cell from a male mammal. D. none of the above. 6. What is the expected number of Barr bodies in an individual with the karyotype XXXYYY? A. 0 B. 1 C. 2 D The genotype X0 produces a A. female in Drosophila and a female in humans. B. female in Drosophila and a male in humans. C. male in Drosophila and a male in humans. D. male in Drosophila and a female in humans. 8. When an organism gains or loses one or more chromosomes but not a complete haploid set, the condition is known as A. polyploidy B. aneuploidy C. triploidy D. trisomy 9. When a diploid organism gains a complete haploid set of chromosomes, the condition is known as A. haploidy B. aneuploidy C. triploidy D. trisomy

3 10. A somatic cell from a human with a monosomy would contain a total of how many chromosomes? A. 46 B. 1 C. 45 D The condition known as cri-du-chat syndrome in humans has a genetic constitution designated as. A. 45, X B. 46,5p- C. triploidy D. trisomy 12. If an organism is heterozygous for a chromosomal inversion, then A. a condition of semisterility will occur in the absence of any crossing-over. B. the organism must be phenotypically abnormal C. chromosome number is likely altered D. meiotic crossovers within the inverted interval will not be recovered in offspring. 13. Diseases associated with genetic anticipation are often caused by A. insertion of foreign DNA into a chromosome. B. expansion of trinucleotide repeats. C. multiple inversions in the X chromosome. D. single translocations in the X chromosome. 14. Trisomy 21, or Down syndrome, usually occurs when there is a normal diploid chromosomal complement of 46 chromosomes plus one (extra) chromosome #21. Such individuals therefore have 47 chromosomes. While there is impaired fertility of both sexes, females are more likely to be fertile than males. Assume that children are born to a female with Down syndrome and a normal 46-chromosome male. What proportion of the offspring would be expected to have Down syndrome? A. One half of the offspring will be expected to have Down syndrome. B. None of the offspring would be expected to have Down syndrome. C. All the children would be expected to have Down syndrome. D. Two-thirds of the offspring would be expected to have Down syndrome.

4 15. While the most frequent form of Down syndrome is caused by a nondisjunction of chromosome #21 during the formation of the mother s egg, on rare occasion a fertilized egg may contain a normal diploid set of chromosomes and yet the individual born shows signs of Down syndrome. This can be explained by A. nondisjunction in Dad s sperm B. a chromosomal inversion C. a balanced translocation D. nondisjunction in early development leading to mosaicism 16. DNA, originally called nuclein, was discovered by A. Hershey and Chase B. Watson and Crick C. Friedrich Miescher D. Klug, Cummings, and Spencer P and 35 S were used in the classic experiment conducted by Hershey and Chase because A. 32 P labels DNA and 35 S labels protein B. 32 P labels protein and 35 S labels DNA C. both radioisotopes label an entire phage including DNA and protein D. 32 P labels DNA and 35 S labels RNA 18. The basic structure of a nucleotide includes which of the following components? A. amino acids. B. base, sugar, phosphate. C. phosphorous and sulfate. D. all of the above. 19. If 10% of the nitrogenous bases in a sample of DNA from a particular organism is thymine, what percentage should be cytosine? A. 15% B. 30% C. 40% D. 35%

5 20. Which of the following clusters of terms accurately describes DNA as it is generally viewed to exist in prokaryotes and eukaryotes? A. Double-stranded, parallel, (A+T)/(C+G)= variable, (A+G)/(C+T)=1.0 B. Single-stranded, antiparallel, (A+T)/(C+G)=1.0, (A+G)/C+T)=1.0 C. Double-stranded, antiparallel, (A+T)/(C+G)=variable, (A+G)/(C+T)=1.0 D. Double-stranded, antiparallel, (A+T)/C+G)=1.0, (A+G)/(C+T)=variable 21. Which diagram shows a nucleotide with a purine base? A. B. C. D. 22. The two strands of a DNA helix are held together (to each other) by A. covalent bonds. B. hydrogen bonds. C. phosphodiester bonds. D. glycosidic bonds. 23. If the sequence of one strand of DNA is 5 -GCATAGGCC-3, then the sequence of the complementary strand is A. 5 -GCATAGGCC-3 B. 5- CCGGATACG-3 C. 5 -CGTATCCGG-3 D. 5 -GGCCTATGC-3

6 24. Which statement is true? A. All DNA is in the form of a right-handed double-helix all of the time. B. DNA has the potential to form a left-handed helix in a test tube under certain conditions. C. Structurally, the two strands of DNA in a helix have the same polarity. D. As a rule, a higher GC content means a lower melting point for a DNA helix. 25. During replication of DNA, strand elongation proceeds A. in a 5' to 3' direction on the leading strand, but in a 3' to 5' direction on the lagging strand. B. in a 3' to 5' direction on the leading strand, but in a 5' to 3' direction on the lagging strand. C. in a 5' to 3' direction on both the leading and lagging strands. D. in a 3' to 5' direction on both the leading and lagging strands. For questions refer to the replication fork depicted below: 5 3 B A 3 B B C Item A is called A. the leading strand. B. primase. C. single strand binding protein. D. an Okazaki fragment. 27. B is most likely: A. an RNA primer. B. a DNA primer. C. DNA polymerase III. D. an exonuclease.

7 28. The enzyme that appears to be inappropriately expressed in cancer cells and helps to maintain the very ends of eukaryotic chromosomes is called A. topoisomerase. B. ligase. C. telomerase. D. terminase. 29. In addition to highly repetitive and unique DNA sequences, a third category of DNA sequences exists. What is it called and what types of elements are involved? A. composite DNA, telomeres and heterochromatin B. dominant DNA, euchromatin and heterochromatin C. multiple gene family DNA, hemoglobin and 5.0S RNA D. middle repetitive DNA, SINEs, LINEs, and VNTRs 30. Chromatin of eukaryotes is organized into repeating interactions with protein octomers called nucleosomes. Nucleosomes are composed of which class of molecules? A. histones B. glycoproteins C. lipids D. nonhistone chromosomal proteins 31. An enzyme that controls supercoiling in DNA is called a A. telomerase B. polymerase C. reverse transcriptase D. topoisomerase 32. Mutations which arise in nature from no particular artificial agent are called A. induced mutations. B. spontaneous mutations. C. chromosomal aberrations. D. cosmic mutations.

8 33. In a transition mutation, A. a pyrimidine substitutes for a purine. B. a purine substitutes for a purine. C. a single nucleotide is inserted D. a translocation occurs. 34. A class of mutations that results in multiple contiguous amino acid changes in proteins is likely to be which of the following? A. base analogue. B. transversion. C. transition. D. frameshift. 35. Ultraviolet light causes pyrimidine dimers to form in DNA. Some individuals are genetically incapable of repairing dimers at normal rates. Such individuals are likely to suffer from A. xeroderma pigmentosum. B. phenylketonuria. C. muscular dystrophy. D. Huntington disease. 36. In mammals, DNA double-strand breaks may be repaired by A. nonhomologous end-joining. B. base excision repair. C. nucleotide excision repair. D. mismatch repair. 37. During mismatch repair in bacteria, the newly synthesized strand is distinguished from the old strand by A. a strand break on the old strand. B. methylation on the new strand. C. methylation on the old strand. D. nothing; the strands cannot be distinguished.

9 38. Virtually all transposable elements in nature A. can t transpose. B. have inverted terminal repeats. C. encode reverse transcriptase. D. transpose only in germline cells. 39. Which of the following is true? A. every amino acid is coded for by a single codon. B. there are more amino acids than there are codons. C. every codon codes for an amino acid. D. each codon in a gene codes for no more than one single amino acid. 40. Which of the following represent three posttranscriptional modifications often seen in the maturation of mrna in eukaryotes? A. 3'-capping, 5'-poly(A) tail addition, splicing. B. removal of exons, insertion of introns, capping. C. 5'-capping, 3'-poly(A) tail addition, splicing. D. 5'-poly(A) tail addition, insertion of introns, capping. That s all!

10 ANSWER KEY Q: A: A A A D D C D B C C B D B A D C A B C C Q: A: D B D B C D A C D A D B B D A A C B D C