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Genetics Exam II

108 Questions
Genetics Quizzes & Trivia

Genetics Exam II

Questions and Answers
  • 1. 
    What observation did Griffith make in his experiment with Streptococcus pneumoniae?
    • A. 

      The mouse survived injection of live virulent (smooth) Streptococcus pneumoniae.

    • B. 

      That DNA is the genetic material.

    • C. 

      The mouse did not survive when injected with a mixture of live, avirulent (smooth) Streptococcus pneumoniae and heat-killed virulent Streptococcus pneumoniae.

    • D. 

      The heat-killed, virulent Streptococcus pneumoniae was lethal to the mouse.

  • 2. 
    What results did Avery, McLeod and McCarty obtain in their experiments with virulent bacteria?
    • A. 

      Protease destroyed the transforming activity.

    • B. 

      DNase destroyed the transforming activity.

    • C. 

      RNase destroyed the transforming activity.

    • D. 

      The transforming principle was too complex and difficult to be purified.

  • 3. 
    Which enzyme makes DNA from an RNA template?
    • A. 

      RNA polymerase

    • B. 

      DNA polymerase

    • C. 

      Reverse Transcriptase

    • D. 

      Replicase

  • 4. 
    In forming a nucleotide, phosphorus is most often attached to the nucleoside at the C-5' position of the sugar.
    • A. 

      True

    • B. 

      False

  • 5. 
    Which of the following is true of thymine?
    • A. 

      Thymine can never be attached to ribose.

    • B. 

      Thymine is the same as 5-methyl uracil.

    • C. 

      Thymine has an amino group at the C-4 position.

    • D. 

      Thymine has a methyl group attached to the N-1 position.

  • 6. 
    Watson and Crick used information from several individuals to construct their model of DNA.  Whose X-ray diffraction studies were critical to their work?
    • A. 

      Linus Pauling

    • B. 

      Phoebus Levene

    • C. 

      Maurice Wilkins

    • D. 

      Rosalind Franklin

  • 7. 
    If a double-stranded sample of DNA has a base composition of 20% guanine, which of the following statements is true?
    • A. 

      The amount of the other purine adenine must also equal 20%.

    • B. 

      The amount of cytosine must be equal to 30% so that the total amount of G + C equals 50%.

    • C. 

      The amount of thymine must equal 30%.

    • D. 

      The ratio of purines to pyrimiidines must be greater than 1.

  • 8. 
    Which of the following statements does not describe Z-DNA?
    • A. 

      The sugar phosphate backbone of Z-DNA assumes a zigzag course through space.

    • B. 

      Z-DNA is a typical of GC-rich sequences.

    • C. 

      It forms a left-handed helix.

    • D. 

      The strands are not antiparallel.

  • 9. 
    RNA differs from DNA in all of the following ways except by
    • A. 

      The sugar molecule.

    • B. 

      The 5'-3' orientation of the polynucleotide strand.

    • C. 

      The presence of uracil.

    • D. 

      The number of different functions performed.

  • 10. 
    Of the following DNA strands in combination with their complementary strands (forming double helices), three undergo a hyperchromic shift with a Tm of about 42*C.  Which one has a Tm of 52*C?
    • A. 

      ATTGAGTGTA

    • B. 

      CTTAAATTTG

    • C. 

      AAATTTGGGA

    • D. 

      TCATGCGATC

  • 11. 
    Which technique can be used to identify the location of genes on a chromosome?
    • A. 

      FISH

    • B. 

      X-ray diffraction analysis

    • C. 

      Reassociation kinetics

    • D. 

      Electrophoresis

  • 12. 
    Which of the following statements about the Cot1/2 or half-association value of DNA fragments is true?
    • A. 

      A longer DNA molecule would associate more quickly (smaller Cot1/2 value).

    • B. 

      Molecules with the highest GC content would associate more slowly.

    • C. 

      DNA with more repeated sequences requires more time to reassociate (smaller Cot value).

    • D. 

      Shorter DNA molecules would associate more quickly (smaller Cot1/2 values).

  • 13. 
    If Avery, MacLeod, and McCarty had determined that the transforming molecule was a protein, what experimental results would not have been observed?
    • A. 

      Heat-killed cultures treated with DNase would transform the R cells.

    • B. 

      Heat-killed cultures treated with protease would not transform the R cells.

    • C. 

      Heat-killed cultures treated with RNase would transform the R cells.

    • D. 

      Heat-killed cultures treated with protease would transform the R cells.

  • 14. 
    What conclusion could be drawn if Hershey and Chase had found only 35S in their bacterial cells?
    • A. 

      No conclusion is possible.

    • B. 

      DNA and protein together serve as the genetic material.

    • C. 

      DNA is the genetic material.

    • D. 

      Protein is the genetic material.

  • 15. 
    To which positions in the sugar of a deoxyribonucleotide can a phosphate be esterified?
    • A. 

      C-3' and C-5'

    • B. 

      C-5'

    • C. 

      C-1', C-2', and C-3'

    • D. 

      C-1' and C-5'

  • 16. 
    Which of the following statements best describes the structure of a DNA molecule?
    • A. 

      DNA is composed of a sugar-phosphate backbone with bases projecting toward the inside of the backbone.

    • B. 

      DNA is composed of a sugar-phosphate backbone with bases projecting toward the outside of the backbone.

    • C. 

      DNA is composed of a sugar-phosphate backbone made up of bases hydrogen-bonded to each other.

    • D. 

      DNA is composed of a deoxynucleoside triphosphate with a base attached to it.

  • 17. 
    If two DNA strands of identical length were analyzed, which of the following statements would be true of their Tm or melting temperature?
    • A. 

      DNA with a low AT content would melt more slowly.

    • B. 

      All DNA strands of equal length have equal melting temperatures.

    • C. 

      The DNA with the greater number of repetitive sequences will melt more slowly (lower Tm).

    • D. 

      DNA with a high GC content must have a lower Tm.

  • 18. 
    Which of the following statements about the difference between DNA and RNA is false?
    • A. 

      RNA is usually much longer than DNA.

    • B. 

      DNA is usually double-stranded.

    • C. 

      RNA has a free 2' hydroxyl group.

    • D. 

      The DNA base composition must have the amount of purines equal to the amount of pyrimidines.

  • 19. 
    Why is it important for a retrovirus to carry its own reverse transcriptase protein instead of making it from its reverse transcriptase gene after it infects a cell?
    • A. 

      It is not important; the virus can make its own reverse transcriptase from its viral RNA after infection.

    • B. 

      The viral reverse transcriptase is different from the host cell's reverse transcriptase.

    • C. 

      The retrovirus must make DNA before it can use the cell's molecular machinery to make reverse transcriptase. Normal cells do not contain reverse transcriptase.

  • 20. 
    Guanine and adenine are purines found in DNA.
    • A. 

      True

    • B. 

      False

  • 21. 
    Which of the following statements about DNA structure is true?
    • A. 

      The pentose sugar in DNA is ribose.

    • B. 

      Nucleic acids are formed through phosphodiester bonds that link nucleosides together.

    • C. 

      Hydrogen bonds formed between the sugar-phosphate backbone of the two DNA chains help to stabilize DNA structure.

    • D. 

      The nucleic acid strands in a DNA molecule are oriented antiparallel to each other, meaning they run in opposite directions.

  • 22. 
    What is the complementary DNA sequence to a 5' ATGCTTGACTG 3'?
    • A. 

      5' TACGAACTGAC 3'

    • B. 

      5' CAGTCAAGCAT 3'

    • C. 

      5' ATGCTTGACTG 3'

    • D. 

      5' ACTCTACGTAG 3'

  • 23. 
    Leaf coloration in the four‑o'clock plant, Mirabilis jalapa, was one of the first examples of cytoplasmic inheritance. If ovules from a white‑leafed branch are pollinated with pollen from a green‑leafed branch, what phenotypes will be observed in the progeny?
    • A. 

      All white‑leafed progeny

    • B. 

      White‑ and green‑leafed progeny

    • C. 

      All variegated‑leafed progeny

    • D. 

      All green‑leafed progeny

  • 24. 
    Leaf coloration in the four‑o'clock plant, Mirabilis jalapa, was one of the first examples of cytoplasmic inheritance. If ovules from a variegated‑leafed branch are pollinated with pollen from a variegated‑leafed branch, what phenotypes will be observed in the progeny?
    • A. 

      All white‑leafed progeny

    • B. 

      White‑ and green‑leafed progeny

    • C. 

      All variegated‑leafed progeny

    • D. 

      All green‑leafed progeny

  • 25. 
    In the yeast Saccharomyces cerevisiaesuppressive petite mutants exhibit Mendelian inheritance because they result from nuclear mutations.
    • A. 

      True

    • B. 

      False

  • 26. 
    Which of the following statements about the endosymbiotic theory is false?
    • A. 

      Mitochondria and chloroplasts arose independently from free‑living bacteria.

    • B. 

      The ancestral bacteria from which mitochondria and chloroplasts are derived were capable of photosynthesis and aerobic respiration.

    • C. 

      The entire genome of the ancestral bacteria has been preserved in present‑day mitochondria and chloroplasts.

    • D. 

      Eukaryotic cells engulfed the ancestral bacteria from which mitochondria and chloroplasts are derived, and the two entities formed a symbiotic relationship.

  • 27. 
    Which term describes the condition in which cells have a variable mixture of organelles with different genetic origins?
    • A. 

      Heteroduplex

    • B. 

      Heteroplasmy

    • C. 

      Heterokaryon

    • D. 

      Heterozygous

  • 28. 
    Which human genetic disease does not exhibit cytoplasmic maternal inheritance?
    • A. 

      Kearns-Sayre syndrome

    • B. 

      Leber's hereditary optic neuropathy

    • C. 

      Hemophilia

    • D. 

      Myoclonic epilepsy

  • 29. 
    Which of the following is an example of infectious heredity?
    • A. 

      Petite mutations in Saccharomyces cerevisiae

    • B. 

      Shell coiling in Limnaea peregra

    • C. 

      Variegation in Mirabilis jalapa

    • D. 

      High female sex ratio in Drosophila bifasciata and Drosophila willistoni

  • 30. 
    The direction of coiling in the snail Limnaea peregra is determined by the genotype of the maternal parent producing the egg, regardless of the progeny's genotype. Which of the following statements correctly describes this trait?
    • A. 

      It is a sex-influenced trait.

    • B. 

      The trait is an example of maternal inheritance.

    • C. 

      It is an X-linked trait.

    • D. 

      The trait is an example of maternal influence.

  • 31. 
    Which of the following crosses could produce a left‑hand coiled shell heterozygote in the snail Limnaea peregra, if the gene D, which codes for right‑hand coiled shells, is dominant to the gene d, which codes for left‑hand coiled shells?
    • A. 

      Left‑hand coiled Dd female × left‑hand coiled dd male

    • B. 

      Left‑hand coiled DD female × left‑hand coiled dd male

    • C. 

      Right‑hand coiled dd female × left‑hand coiled DD male

    • D. 

      Left‑hand coiled DD female × right‑hand coiled dd male

  • 32. 
    Which of the following crosses could produce a right‑hand coiled shell heterozygote in the snail Limnaea peregra, if the gene D, which codes for right‑hand coiled shells, is dominant to the gene d, which codes for left‑hand coiled shells?
    • A. 

      Left‑hand coiled DD female × right‑hand coiled DD male

    • B. 

      Right‑hand coiled dd female × right‑hand coiled dd male

    • C. 

      Left‑hand coiled dd female × right‑hand coiled DD male

    • D. 

      Right‑hand coiled Dd female × right‑hand coiled Dd male

  • 33. 
    Organelle heredity, maternal effect, and infectious heredity are all examples of extranuclear inheritance, which is the transmission of genetic information to offspring through the cytoplasm rather than through the nucleus.
    • A. 

      True

    • B. 

      False

  • 34. 
    Which of the following phenotypic descriptions does not describe a mitochondrial trait?
    • A. 

      Petite in Saccharomyces cerevisiae

    • B. 

      Kearns–Sayre syndrome in humans

    • C. 

      Poky in Neurospora crassa

    • D. 

      Streptomycin resistance in Chlamydomonas reinhardi

  • 35. 
    Leber's hereditary optic neuropathy is caused by a mutation in the mitochondrial gene encoding NADH dehydrogenase. The trait exhibits cytoplasmic inheritance and is passed along maternal lines. Often, however, both parents of an affected individual are phenotypically normal, and there is no family history of the disease. What is the most likely explanation for this observation?
    • A. 

      The mother was heterozygous, and the gamete that formed the zygote did not carry the mutant allele.

    • B. 

      The mother exhibited incomplete penetrance for the trait.

    • C. 

      The disease does not affect females, only males.

    • D. 

      A new mutation arose in the mitochondrial genome.

  • 36. 
    What proportions of progeny would be expected from a cross between streptomycin‑sensitive mt+ and streptomycin‑resistant mt strains of the algaChlamydomonas reinhardi?
    • A. 

      All streptomycin‑sensitive mt+

    • B. 

      All streptomycin‑resistant mt–

    • C. 

      One‑half streptomycin‑resistant mt+ and one‑half streptomycin‑resistant mt–

    • D. 

      One‑half streptomycin‑sensitive mt+and one‑half streptomycin‑sensitive mt–

  • 37. 
    Which of the following statements about maternal inheritance is true?
    • A. 

      In maternal inheritance, the phenotype of the progeny does not necessarily depend on the individual's genotype but on the genotype of the maternal parent.

    • B. 

      In maternal inheritance, reciprocal crosses give identical results but with different ratios among male and female progeny.

    • C. 

      In maternal inheritance, the genes are linked to the X chromosome.

    • D. 

      In maternal inheritance, a trait is transmitted through the ooplasm, because the mitochondria and chloroplasts of the zygote derive from the ooplasm.

  • 38. 
    What is the general term for a condition in which the chromosome number is not a multiple of a complete set?
    • A. 

      Triploidy

    • B. 

      Aneuploidy

    • C. 

      Polyploidy

    • D. 

      Trisomy

  • 39. 
    Which gametes will be produced if nondisjunction occurs during the second meiotic division?
    • A. 

      All haploid gametes

    • B. 

      Two haploid gametes, one diploid gamete, and one gamete missing a copy of one of the chromosomes

    • C. 

      Two diploid gametes and two haploid gametes

    • D. 

      All trisomic gametes

  • 40. 
    What is the specific term that describes the loss of a single chromosome (2n - 1)?
    • A. 

      Monosomy

    • B. 

      Trisomy

    • C. 

      Aneuploidy

    • D. 

      Monoploidy

  • 41. 
    Which genetic disease is caused by a trisomy for chromosome 13?
    • A. 

      Cri-du-chat syndrome

    • B. 

      Edwards syndrome

    • C. 

      Down syndrome

    • D. 

      Patau syndrome

  • 42. 
    Which human chromosomes have been observed in an aneuploid condition in fetuses?
    • A. 

      Chromosomes 21, 18, and 13

    • B. 

      Only the sex chromosomes X and Y

    • C. 

      X, Y, and chromosome 21

    • D. 

      All chromosomes

  • 43. 
    Which term specifically refers to the gain of extra chromosome sets from individuals of the same species?
    • A. 

      Allopolyploidy

    • B. 

      Autopolyploidy

    • C. 

      Euploidy

    • D. 

      Triploidy

  • 44. 
    Chromosomal aberrations may be characterized by all of the following except
    • A. 

      Chromosome loss

    • B. 

      Translocations

    • C. 

      Frameshift mutations

    • D. 

      Inversions

  • 45. 
    The hypothesis that gene duplication is essential to evolution is supported by the existence of
    • A. 

      Fragile sites.

    • B. 

      Gene families.

    • C. 

      Intercalary deletions.

    • D. 

      Inversions.

  • 46. 
    Which of the following human genetic diseases is caused by a segmental deletion (partial monosomy)?
    • A. 

      Fragile X syndrome

    • B. 

      Turner syndrome

    • C. 

      Cri-du-chat syndrome

    • D. 

      Edwards syndrome

  • 47. 
    What distinguishes paracentric inversions from pericentric inversions?
    • A. 

      Inclusion of the centromere in the inversion.

    • B. 

      One suppresses crossovers; the other encourages crossovers.

    • C. 

      The placement of the centromere in the inversion.

    • D. 

      The formation of dicentric bridges.

  • 48. 
    Why would the transmission of Down syndrome resulting from a Robertsonian translocation be unaffected by the age of the mother?
    • A. 

      Down syndrome resulting from a Robertsonian translocation does not result from nondisjunction, which is affected by age.

    • B. 

      This statement is incorrect; the age of the mother does affect the transmission of Down syndrome resulting from Robertsonian translocations.

    • C. 

      Mothers with a Robertsonian translocation never have children.

    • D. 

      Robertsonian translocations occur only in young mothers.

  • 49. 
    Fragile X syndrome is thought to be caused by the inactivation of a gene spanning the fragile region on the X chromosome due to a large number of trinucleotide repeats just upstream from the coding sequence of the gene.
    • A. 

      True

    • B. 

      False

  • 50. 
    Which of the following statements about nondisjunction is false?
    • A. 

      It separates maternal from paternal chromatids.

    • B. 

      It occurs more frequently in human females over age 35.

    • C. 

      It may fail to separate maternal chromatids from one another or paternal chromatids from one another.

    • D. 

      It may fail to separate maternal from paternal chromatids.

  • 51. 
    Which term best describes an individual with Klinefelter syndrome?
    • A. 

      Triploid

    • B. 

      Aneuploid

    • C. 

      Polyploid

    • D. 

      Euploid

  • 52. 
    Which human aneuploid condition does not involve a sex chromosome?
    • A. 

      Turner syndrome

    • B. 

      Familial Down syndrome

    • C. 

      Fragile X syndrome

    • D. 

      Trisomy 21

  • 53. 
    • A. 

      72

    • B. 

      36

    • C. 

      9

    • D. 

      18

  • 54. 
    The normally cultivated cotton plant is a tetraploid (52 chromosomes). How many chromosomes did the probable ancestral haploid have?
    • A. 

      52

    • B. 

      26

    • C. 

      13

    • D. 

      104

  • 55. 
    Which condition produced from an autosomal trisomy results in survival to adulthood?
    • A. 

      Patau syndrome

    • B. 

      Edwards syndrome

    • C. 

      Cri-du-chat syndrome

    • D. 

      Down syndrome

  • 56. 
      Which of the following terms can be used to describe Down syndrome?
    • A. 

      Triploid and aneuploid

    • B. 

      Trisomy and polyploid

    • C. 

      Trisomy and aneuploid

    • D. 

      Triploid and polyploid

  • 57. 
    How can duplications arise?
    • A. 

      A chromosome break and exchange

    • B. 

      Uneven crossing over during meiotic prophase

    • C. 

      Spindle failure during chromosome separation

    • D. 

      Loss of a telomere

  • 58. 
    A child is born with Down syndrome. Analysis of his karyotype shows two number 21 chromosomes, a single number 18 chromosome, and an additional large chromosome about the size of chromosome 3. Which of the following conclusions can be drawn from the karyotype?
    • A. 

      The large chromosome represents a deleted chromosome number 1.

    • B. 

      The large chromosome represents a Robertsonian fusion between chromosomes 21 and 18.

    • C. 

      There is too little information about chromosome 21 to draw a conclusion.

    • D. 

      The large chromosome represents an extra chromosome 3.

  • 59. 
      The incidence of Down syndrome, also known as trisomy 21, increases with increasing maternal age. Which of the following errors most likely produces this condition?
    • A. 

      Nondisjunction during either meiosis I or II in the male gamete

    • B. 

      Nondisjunction during meiosis I in either the male and female gamete

    • C. 

      Nondisjunction during meiosis II in either the male and female gamete

    • D. 

      Nondisjunction during either meiosis I or II in the female gamete

  • 60. 
    Females with only one X chromosome do not develop; this condition is lethal.
    • A. 

      True

    • B. 

      False

  • 61. 
    A cross between a tetraploid and a diploid member of the same species will produce offspring that can undergo sexual reproduction.
    • A. 

      True

    • B. 

      False

  • 62. 
    • A. 

      Diploid number of 5

    • B. 

      Diploid number of 12

    • C. 

      Haploid number of 5

    • D. 

      Haploid number of 10

  • 63. 
    What phenotype would be expected in balanced translocation heterozygotes in the absence of position effects?
    • A. 

      Normal, even though they have too much genetic material

    • B. 

      Abnormal, because they have too much genetic material

    • C. 

      Normal, because they have a normal amount of genetic material

    • D. 

      Abnormal, because they lack some genetic material

  • 64. 
    Which of the following syndromes is not paired with its causative chromosomal aberration?
    • A. 

      Fragile X syndrome-deletion

    • B. 

      Cri-du-chat syndrome-deletion

    • C. 

      Down syndrome-Robertsonian translocation

    • D. 

      Huntington's disease-duplication

  • 65. 
    Why do some organisms use both sexual and asexual reproduction?
    • A. 

      The two modes of reproduction maximize the genetic variation within a species.

    • B. 

      The organisms are hermaphroditic.

    • C. 

      The two modes of reproduction are favored under different conditions.

    • D. 

      The organisms are monoecious.

  • 66. 
    The sporophyte stage in plants
    • A. 

      Occurs only within the megaspore mother cell.

    • B. 

      Is diploid and produces haploid spores.

    • C. 

      Is linked to the haploid phase via mitosis.

    • D. 

      Is diploid and produces diploid spores.

  • 67. 
    Which of the following statements about the roundworm C. elegans is false?
    • A. 

      No individuals are exclusively female.

    • B. 

      The lineage of every adult cell can be traced back to its embryonic origins.

    • C. 

      Adults are very simple, consisting of approximately 1000 cells.

    • D. 

      Males have a Y chromosome, and hermaphrodites have an X chromosome.

  • 68. 
    A human with XXY sex chromosomes is female because she has two X chromosomes.
    • A. 

      True

    • B. 

      False

  • 69. 
    Which of the following statements about XYY males is true?
    • A. 

      They are generally taller than average.

    • B. 

      They are sterile.

    • C. 

      They are likely to end up in prison.

    • D. 

      They have underdeveloped secondary sex characteristics.

  • 70. 
    How does the Y chromosome determine maleness in humans?
    • A. 

      By containing the autosomal genes responsible for the SRY effects

    • B. 

      By containing the genes for steroid metabolism

    • C. 

      By containing a gene coding for the TDF, which directs the development of fetal gonads

    • D. 

      By containing the structural genes for testes production

  • 71. 
    Which of the following statements about individuals with Klinefelter syndrome or Turner syndrome is false?
    • A. 

      Individuals with either syndrome have 44 autosomes.

    • B. 

      Both syndromes can be identified by a karyotype.

    • C. 

      Individuals with either syndrome are both identified as females.

    • D. 

      Both syndromes result from nondisjunction.

  • 72. 
    What are pseudoautosomal regions on the sex chromosomes?
    • A. 

      Regions of the X and Y chromosomes that don't recombine during meiosis

    • B. 

      Homologous regions of the X and Y chromosomes

    • C. 

      Homozygous regions of autosomal chromosomes

    • D. 

      Hemizygous regions of the X and Y chromosomes

  • 73. 
    What is one explanation for the difference between the primary sex ratio and the secondary sex ratio in humans?
    • A. 

      Women live significantly longer than men.

    • B. 

      Y-bearing sperm are better swimmers than X-bearing sperm.

    • C. 

      More boys die during infancy than girls.

    • D. 

      There is disproportionate death of female fetuses prior to birth.

  • 74. 
    Which of the following statements about Barr bodies is true?
    • A. 

      They contain no DNA.

    • B. 

      They are inactivated Y chromosomes.

    • C. 

      They ensure that males and females have equal "doses" of the genes on the X chromosome.

    • D. 

      They are visible only in males.

  • 75. 
    A human with the karyotype 49,XXXYY forms two Barr bodies.
    • A. 

      True

    • B. 

      False

  • 76. 
    The paternal X is always inactivated for dosage compensation in placental mammals.
    • A. 

      True

    • B. 

      False

  • 77. 
    How is sex determined in Drosophila?
    • A. 

      By the ratio of the number of X chromosomes to the number of sets of autosomes

    • B. 

      By the ratio of the number of Y chromosomes to the number of sets of autosomes

    • C. 

      By the ratio of the number of X chromosomes to the number of autosomes

    • D. 

      By the ratio of the number of Y chromosomes to the number of autosomes

  • 78. 
    In a sexually reproducing diploid species, gametes must be
    • A. 

      Diploid.

    • B. 

      Male or female.

    • C. 

      Produced via mitosis.

    • D. 

      Haploid.

  • 79. 
    Which of the following statements about double fertilization is true?
    • A. 

      It results in individuals with an extra copy of one of the sex chromosomes.

    • B. 

      It is the mechanism by which monozygotic, but not dizygotic, twins are produced.

    • C. 

      It is the mechanism by which two sperm nuclei fertilize an oocyte and two endosperm nuclei, respectively.

    • D. 

      It is the mechanism by which dizygotic, but not monozygotic, twins are produced.

  • 80. 
    All of the following are mechanisms by which sex can be determined except
    • A. 

      The presence of two X chromosomes or an X and a Y chromosome.

    • B. 

      The ratio of X chromosomes to the number of sets of autosomes.

    • C. 

      The temperature at which the eggs are incubated.

    • D. 

      The number of Barr bodies present.

  • 81. 
    What is the diploid chromosome number of an individual with both Klinefelter syndrome and Down syndrome (three copies of chromosome 21)?
    • A. 

      45

    • B. 

      46

    • C. 

      47

    • D. 

      48

  • 82. 
    In maize, there are mutant genes that confer male sterility to all of the offspring of the female parent carrying this genotype. This genetic information is not found on any of the chromosomes that make up the maize genome. What is the most likely mode of inheritance for these genes?
    • A. 

      Transgenic inheritance

    • B. 

      Extrachromosomal inheritance

    • C. 

      Pseudoinheritance

    • D. 

      Biparental inheritance

  • 83. 
    The effect of Barr body formation in mammals is that
    • A. 

      Females are mosaics for homozygous X-linked genes.

    • B. 

      Females are mosaics for heterozygous X-linked genes.

    • C. 

      Males are mosaics for hemizygous X-linked genes.

    • D. 

      Females are mosaics for heterozygous autosomal genes.

  • 84. 
    Which of the following statements about dosage compensation is true?
    • A. 

      It is a problem in species that have more autosomes than sex chromosomes.

    • B. 

      It cannot be directed by a master switch that enhances X-chromosome activity.

    • C. 

      Its mechanism is the same in all animals.

    • D. 

      It must occur when one sex has more copies of a gene or genes than the other sex.

  • 85. 
    Why is it easier to identify spontaneous mutations in bacteria than in most eukaryotes?
    • A. 

      They can be induced via exposure to the bacteriophage T1.

    • B. 

      They are expressed directly in descendant cells because bacteria are haploid.

    • C. 

      They occur at a much higher frequency.

    • D. 

      They are visible as color changes within a bacterial plaque.

  • 86. 
    An E. coli nutritional mutant is described as an auxotroph, which requires minimal medium with supplementation of an organic carbon source or inorganic ion for growth.
    • A. 

      True

    • B. 

      False

  • 87. 
    What limits E. coli growth within a medium culture?
    • A. 

      All of these choices

    • B. 

      Physical space

    • C. 

      Carbon dioxide

    • D. 

      Nutrients and oxygen

  • 88. 
    Which of the following statements is not true of Hfr bacteria?
    • A. 

      They function as the donor in crosses with F− bacteria.

    • B. 

      They are derived from F+ bacteria.

    • C. 

      They frequently convert recipient bacteria to F+ cells.

    • D. 

      They function as the donor only in crosses with F− bacteria and are so called because they result in high frequency recombination.

  • 89. 
    What is a merozygote?
    • A. 

      A haploid bacterial cell

    • B. 

      The result of sexual reproduction between two bacteria cells

    • C. 

      A partially diploid bacterial cell

    • D. 

      A zygote formed from a bacteriophage and a bacterial cell

  • 90. 
    The fertility factor is a mobile genetic element called a plasmid that contains genes for directing gene transfer between bacterial cells.
    • A. 

      True

    • B. 

      False

  • 91. 
    Which of the following statements about cotransformation is true?
    • A. 

      Unlinked genes are passed simultaneously from one cell to another.

    • B. 

      Two bacterial cells within a culture are transformed by the same genetic material.

    • C. 

      A bacterial cell receives two adjacent genes on a single piece of DNA from the medium.

    • D. 

      It is not uncommon for the entire bacterial chromosome and F factor to be passed from one cell to another.

  • 92. 
    All of the following statements about bacteriophages are true except that
    • A. 

      They are viruses.

    • B. 

      They can pick up bacterial genes during the process of infecting a bacterial cell.

    • C. 

      Within their heads, they can pack the main chromosome from one cell and transfer it to another.

    • D. 

      They use the metabolic machinery of a bacterial cell to produce more copies of themselves.

  • 93. 
    A plaque assay detects the number of bacterial auxotrophs on a plate.
    • A. 

      True

    • B. 

      False

  • 94. 
    Which of the following statements best describes lysogeny?
    • A. 

      An infected bacterial cell is immediately ruptured following rapid replication of the phage DNA.

    • B. 

      A phage infects a bacterium, and the phage DNA lives symbiotically within the F‑factor plasmid in the cell.

    • C. 

      Viral DNA is integrated into the bacterial DNA and passed on harmlessly with each round of replication and cell division.

    • D. 

      Chemical or UV light treatment renders the viral DNA harmless to the bacterial cell.

  • 95. 
    What is transduction?
    • A. 

      Viral‑mediated viral recombination

    • B. 

      Bacterial‑mediated bacterial recombination

    • C. 

      Viral‑mediated bacterial recombination

    • D. 

      Bacterial‑mediated viral recombination

  • 96. 
    What does intergenic mapping involve?
    • A. 

      Mapping genes by observing recombination between a virus and a bacterial genome

    • B. 

      Gene mapping within a species

    • C. 

      Mapping between genes

    • D. 

      Mapping genes by observing recombination between two different virus genomes

  • 97. 
    How does recombination in bacteria differ from recombination in eukaryotes?
    • A. 

      Sister chromatids, not homologous chromosomes, exchange information during recombination.

    • B. 

      A portion of DNA from one genome is replaced with homologous DNA from another strain of bacteria.

    • C. 

      Only the plasmid DNA goes through recombination in prokaryotes.

    • D. 

      Recombination does not occur in prokaryotes.

  • 98. 
    How is genetic information transferred during conjugation?
    • A. 

      Bidirectionally between two cells

    • B. 

      From one bacterium to another

    • C. 

      With the help of a viral go‑between

    • D. 

      From one cell into the culture medium, where it is taken up by another cell

  • 99. 
    When a bacterial cell is transformed, after one round of cell division, only one of the two resulting cells contains new genetic material because
    • A. 

      The original gene, still floating in the cytoplasm, may be used when replicating the chromosome.

    • B. 

      At transformation, a heteroduplex is formed that alters only one strand of the DNA, leaving the other unchanged.

    • C. 

      Many cells reject newly integrated genes.

    • D. 

      Transformed cells are initially heterozygous.

  • 100. 
    Which of the following elements is not involved in conjugation?
    • A. 

      Transformation

    • B. 

      Sex pilus

    • C. 

      Bacterial contact

    • D. 

      Plasmids

  • 101. 
    Bacterial cells are always haploid unless
    • A. 

      The F factor is removed from the chromosome, taking chromosomal genes with it, and the cell then transfers its F plasmid to another cell.

    • B. 

      They are simultaneously infected by two Hfr strains.

    • C. 

      None of these choices. They are always haploid.

    • D. 

      They are infected with a transforming phage that has been incubated with bacteria from the same strain.

  • 102. 
    Hfr bacterial cells exhibit high levels of gene transfer because
    • A. 

      They do not require conjugation for gene transfer.

    • B. 

      Rather than existing as an isolated plasmid, the F factor is incorporated into the bacterial chromosome.

    • C. 

      They contain two distinct F factors.

    • D. 

      They induce the production of significantly more sex pili than normal F+ cells.

  • 103. 
    In an Hfr mating with an Fcell, why doesn't the recipient cell always become an Hfr or F+ cell?
    • A. 

      F−cells become F+ or Hfr cells only if the mating is interrupted before a complete chromosome is transferred.

    • B. 

      Some Hfr cells do not carry the F factor.

    • C. 

      Hfr cells often carry the F factor in a free‑floating plasmid that is not transferred.

    • D. 

      The F factor is the last part of the chromosome to be transferred.

  • 104. 
    Forty-eight plaques were counted on a plate when 0.1 ml of bacteriophage-infected bacteria from a 10−6 dilution of a 10‑ml culture was plated. The original bacteriophage density was
    • A. 

      48 × 10^7

    • B. 

      4.8 × 10^−7

    • C. 

      48 × 10^−6

    • D. 

      4.8 × 10^6

  • 105. 
    Which of the following statements about conjugation is true?
    • A. 

      DNA is transferred from an F+ cell to an F− cell.

    • B. 

      Only competent cells can undergo conjugation.

    • C. 

      The F factor is an element that is found in the chromosome of an F+ cell.

    • D. 

      One strand of DNA from an F+ cell integrates into the chromosome of an F− cell, and the other strand is degraded.

  • 106. 
    How is a merozygote formed?
    • A. 

      The F factor is inserted into the chromosome of an F− cell, causing it to become an Hfr strain.

    • B. 

      The F factor is excised from the chromosome of an Hfr strain, causing it to revert to F−.

    • C. 

      The F factor and several adjacent genes are excised from the chromosome of an F+ cell and transferred to an F− strain.

    • D. 

      The F factor is inserted into the chromosome of an F+ cell, causing it to revert to F−.

  • 107. 
    Which of the following statements about the T4 lytic life cycle is false?
    • A. 

      The phage produces lysozyme, which ruptures the host cell wall and releases newly formed viral particles.

    • B. 

      The bacterial DNA is degraded.

    • C. 

      The phage takes over the protein synthesis machinery of the bacteria.

    • D. 

      The phage DNA is injected into the host and integrates into the bacterial chromosome.

  • 108. 
    What results would be expected from a plaque assay if the dilution factor of the phage‑infected culture were too low?
    • A. 

      The plate would have a few plaques.

    • B. 

      The entire lawn of bacteria would be lysed.

    • C. 

      None of these choices

    • D. 

      The plate would have no plaques.