19

Front 1

19-1 Organisms that reproduce sexually ________________________.

Back 1

(d) undergo a sexual reproductive cycle that involves an alternation of haploid cells with the generation of diploid cells.

Hint 1

(a) must be haploid, unlike organisms that reproduce asexually.
(b) can reproduce only with a partner that carries the same alleles.
(c) create zygotes that are genetically identical to each other.
(d) undergo a sexual reproductive cycle that involves an alternation of haploid cells with the generation of diploid cells.

Front 2

19-2 Which of the following statements is true?

Back 2

(a) Another name for the fertilized egg cell is the zygote.

Hint 2

(a) Another name for the fertilized egg cell is the zygote.
(b) Diploid organisms reproduce only sexually.
(c) All sexually reproducing organisms must have two copies of every chromosome.
(d) Gametes have only one chromosome.

Front 3

19-3 Which of the following statements is false?

Back 3

(b) Mutations in somatic cells are passed on to individuals of the next generation.

Hint 3

(a) Asexual reproduction typically gives rise to offspring that are genetically identical.
(b) Mutations in somatic cells are passed on to individuals of the next generation.
(c) Sexual reproduction allows for a wide variety of gene combinations.
(d) Gametes are specialized sex cells.

Front 4

19-4 Somatic cells ___________________________.

Back 4

(c) leave no progeny.

Hint 4

(a) are not necessary for sexual reproduction in all eukaryotic organisms.
(b) are used to produce germ-line cells when organisms reach sexual maturity
(c) leave no progeny.
(d) do not contain sex chromosomes.

Front 5

19-5 Which of the following statements about the benefits of sexual reproduction is false?

Back 5

a) Sexual reproduction permits enhanced survival because the gametes that carry alleles enhancing survival in harsh environments are used preferentially during fertilization.

Hint 5

(a) Sexual reproduction permits enhanced survival because the gametes that carry alleles enhancing survival in harsh environments are used preferentially during fertilization.
(b) Unicellular organisms that can undergo sexual reproduction have an increased ability to adapt to harsh environments.
(c) Sexual reproduction reshuffles genes, which is thought to help species survive in novel or varying environments.
(d) Sexual reproduction can speed the elimination of deleterious alleles.

Front 6

19-7 During sexual reproduction, novel mixtures of alleles are generated. This is because ______.

Back 6

(d) during meiosis, the segregation of homologs is random such that different gametes end up with different alleles of each gene.

Hint 6

(a) in all diploid species, two alleles exist for every gene.
(b) a diploid individual has two different alleles for every gene.
(c) every gamete produced by a diploid individual has several different alleles of a single gene.
(d) during meiosis, the segregation of homologs is random such that different gametes end up with different alleles of each gene.

Front 7

19-8 Which of the following does not describe a situation of asexual reproduction?

Back 7

(c) Using in vitro fertilization to combine a sperm and an egg to create an embryo.

Hint 7

(a) A bacterium multiplying by simple cell division.
(b) Using a part of a plant to create a new independent plant.
(c) Using in vitro fertilization to combine a sperm and an egg to create an embryo.
(d) The parthenogenetic development of eggs produced by some species of lizards.

Front 8

19-9 Both budding yeast and the bacteria E. coli are unicellular life. Which of the following statements explains why budding yeast can undergo sexual reproduction while E. coli cannot.

Back 8

(a) Unlike E. coli, budding yeast can alternate between a diploid state and a haploid state.

Hint 8

(a) Unlike E. coli, budding yeast can alternate between a diploid state and a haploid state.
(b) Unlike E. coli, budding yeast cannot multiply by undergoing cell division.
(c) Unlike E. coli, haploid budding yeast cells can undergo meiosis to produce the gametes necessary for sexual reproduction.
(d) E. coli DNA is unable to undergo homologous recombination, making it incapable of producing gametes.

Front 9

19-14 The formation of a bivalent during meiosis ensures that _______.

Back 9

(b) all four sister chromatids remain together until the cell is ready to divide.

Hint 9

(a) one chromatid from the mother and one chromatid from the father will segregate together during meiosis I.
(b) all four sister chromatids remain together until the cell is ready to divide.
(c) recombination will occur between identical sister chromatids.
(d) the sex chromosomes, which are not identical, will line up separately at the metaphase plate during meiosis I.

Front 10

19-15 Imagine meiosis in a diploid organism that only has a single chromosome. Like most diploid organisms, it received one copy of this chromosome from each of its parents and the two homologs are genetically distinct. If only a single homologous recombination event occurs during meiosis, which of the following choices below correctly describes the four gametes formed.

Back 10

(d) Two of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell, while two of the gametes will have chromosomes that are different.

Hint 10

(a) None of the gametes will contain chromosomes identical to the chromosomes found in the original diploid cell.
(b) All four of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell.
(c) Three of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell, while one of the gametes will have chromosomes that are different.
(d) Two of the gametes will have chromosomes identical to the chromosomes found in the original diploid cell, while two of the gametes will have chromosomes that are different.

Front 11

19-16 There are organisms that go through meiosis but do not undergo recombination when forming haploid gametes. Which of the following statements correctly describes the gametes produced by such an organism. (Assume that these organisms are diploid, that each of the two homologous chromosomes are genetically distinct as typically found in the wild, and that these organisms have more than one chromosome.)

Back 11

(c) This organism could potentially produce 2n genetically distinct gametes, where n is its haploid number of chromosomes.

Hint 11

(a) All gametes formed during a single meiosis will be identical.
(b) Due to the random assortment of homologs, each of the gametes formed during a single meiosis will be different.
(c) This organism could potentially produce 2n genetically distinct gametes, where n is its haploid number of chromosomes.
(d) The fusion of any two gametes produced by such an organism that does not undergo recombination during meiosis will create a cell that is genetically identical to that individual.

Front 12

19-19 In the absence of recombination, how many genetically different types of gamete can an organism with five homologous chromosome pairs produce?

Back 12

(c) 32

Hint 12

(a) 5
(b) 10
(c) 32
(d) 64

Front 13

19-20 Which of the following statements most correctly describes meiosis?

Back 13

(b) Meiosis involves a single round of DNA replication followed by four successive

Hint 13

(a) Meiosis involves two rounds of DNA replication followed by a single cell division.
(b) Meiosis involves a single round of DNA replication followed by four successive cell divisions.
(c) Meiosis involves four rounds of DNA replication followed by two successive cell divisions.
(d) Meiosis involves a single round of DNA replication followed by two successive cell divisions.

Front 14

19-21 A diploid cell containing 32 chromosomes will make a haploid cell containing ___ chromosomes.

Back 14

(b) 16

Hint 14

(a) 8
(b) 16
(c) 30
(d) 64

Front 15

19-24 You examine a worm that has two genders: males that produce sperm and hermaphrodites that produce both sperm and eggs. The diploid adult has four homologous pairs of chromosomes that undergo very little recombination. Given a choice, the hermaphrodites prefer to mate with males, but just to annoy the worm, you pluck a hermaphrodite out of the wild and fertilize its eggs with its own sperm. Assuming that all the resulting offspring are viable, what fraction do you expect to be genetically identical to the parent worm? Assume that each chromosome in the original hermaphrodite is genetically distinct from its homolog

Back 15

(c) 1 over 16

Hint 15

(a) all
(b) none
(c) 1 over 16
(d) 1 over 25

Front 16

19-25 Which of the following statements about meiosis is true?

Back 16

(a) During meiosis, the paternal chromosomes pair with the maternal chromosomes before lining up at the metaphase plate.

Hint 16

(a) During meiosis, the paternal chromosomes pair with the maternal chromosomes before lining up at the metaphase plate.
(b) Unicellular organisms that have a haploid state undergo meiosis instead of mitosis during cell division.
(c) Meiosis produces four genetically identical cells.
(d) In general, meiosis is faster than mitosis.

Front 17

19-27 During recombination ________________________.

Back 17

(b) chiasmata hold chromosomes together.

Hint 17

(a) sister chromatids undergo crossing-over with each other.
(b) chiasmata hold chromosomes together.
(c) one crossover event occurs for each pair of human chromosomes.
(d) the synaptonemal complex keeps the sister chromatids together until anaphase II.

Front 18

19-28 After the first meiotic cell division ________________________.

Back 18

(b) cells are produced that contain the same number of chromosomes as somatic cells.

Hint 18

(a) two haploid gametes are produced.
(b) cells are produced that contain the same number of chromosomes as somatic cells.
(c) the number of chromosomes will vary depending on how the paternal and maternal chromosomes align at the metaphase plate.
(d) DNA replication occurs.

Front 19

19-31 In mammals, there are two sex chromosomes, X and Y, which behave like homologous chromosomes during meiosis. Normal males have one X chromosome and one Y chromosome, and normal females have two X chromosomes. Males with an extra Y chromosome (XYY) are found occasionally. Which of the following could give rise to such an XYY male? Explain your answer.

Back 19

(b) nondisjunction in the second meiotic division of spermatogenesis; normal meiosis

Hint 19

(a) nondisjunction in the first meiotic division of spermatogenesis; normal meiosis in the mother
(b) nondisjunction in the second meiotic division of spermatogenesis; normal meiosis in the mother
(c) nondisjunction in the first meiotic division of oogenesis; normal meiosis in the father
(d) nondisjunction in the second meiotic division of oogenesis; normal meiosis in the father

Front 20

19-32 Which of the following would not lead to aneuploidy during meiosis?

Back 20

(c) a reciprocal rearrangement of parts between nonhomologous chromosomes (for example, the left arm of Chromosome 2 exchanging places with the right arm of Chromosome 3)

Hint 20

(a) sister chromatids segregating inappropriately
(b) non-sister chromatids segregating inappropriately
(c) a reciprocal rearrangement of parts between nonhomologous chromosomes (for example, the left arm of Chromosome 2 exchanging places with the right arm of Chromosome 3)
(d) an extra set of chromosomes produced during S phase (for example, if paternal Chromosome 3 were replicated twice)

Front 21

19-33 A single nondisjunction event during meiosis ___________________.

Back 21

(d) will involve the production of two normal gametes if it occurs during meiosis II.

Hint 21

(a) will block recombination.
(b) will occur only during meiosis II.
(c) cannot occur with sex chromosomes.
(d) will involve the production of two normal gametes if it occurs during meiosis II.

Front 22

19-35 During fertilization in humans, _______________________.

Back 22

a) a wave of Ca2+ ions is released in the fertilized egg’s cytoplasm.

Hint 22

(a) a wave of Ca2+ ions is released in the fertilized egg’s cytoplasm.
(b) only one sperm binds to the unfertilized egg.
(c) a sperm moves in a random fashion until it encounters an egg.
(d) several sperm pronuclei compete in the cytoplasm to fuse with the egg nucleus.

Front 23

19-37 Which of the following statements about Mendel’s experiments is false?

Back 23

(d) All traits that Mendel studied were recessive.

Hint 23

(a) The pea plants could undergo both cross-fertilization and self-fertilization.
(b) The true-breeding strains were homozygous for the traits that Mendel examined.
(c) The egg can carry either the allele from the maternal or the paternal chromosome.
(d) All traits that Mendel studied were recessive.

Front 24

19-38 Which of the following could be considered a true-breeding strain for the seed-shape phenotype? (See Figure Q19-38.)

Back 24

(b) all of the wrinkle-seeded plants produced in the F2 generation

Hint 24

(a) all of the round-seeded plants produced in the F2 generation
(b) all of the wrinkle-seeded plants produced in the F2 generation
(c) all of the round-seeded plants produced in the F1 generation
(d) half of the round-seeded plants produced in the F2 generation

Front 25

19-39 If you crossed the round-seeded plants obtained in the F1 generation with a true-breeding strain of round-seeded plants, how many wrinkle-seeded plants would you expect to obtain in the next generation? (See Figure Q19-38.)

Back 25

(a) none

Hint 25

(a) none
(b) 25%
(c) 75%
(d) all

Front 26

19-40 If you crossed the round-seeded plants obtained in the F1 generation with a true-breeding strain of wrinkle-seeded plants, how many round-seeded plants would you expect to obtain in the next generation? (See Figure Q19-38.)

Back 26

(b) 50%

Hint 26

(a) 25%
(b) 50%
(c) 75%
(d) 100%

Front 27

19-41 Which of the following statements about the round-seeded pea plants obtained in the F2 generation is false? (See Figure Q19-38.)

Back 27

(c) We expect 25% of these plants to be homozygous for the seed-shape allele.

Hint 27

(a) These plants are phenotypically identical for seed shape.
(b) Two-thirds of these plants are expected to be heterozygous for the seed-shape allele.
(c) We expect 25% of these plants to be homozygous for the seed-shape allele.
(d) If these plants were crossed to wrinkle-seeded plants, some of these plants would produce only round-seeded plants.

Front 28

19-42 Which of the following statements about the experiment diagrammed in Figure Q19-38 is true?

Back 28

(a) If you crossed all the round-seeded pea plants from the F2 generation with true-breeding wrinkle-seeded pea plants, you would get more round-seeded pea plants in the next generation than if you crossed all the round-seeded pea plants from the F1 generation with true-breeding wrinkle-seeded pea plants.

Hint 28

(a) If you crossed all the round-seeded pea plants from the F2 generation with true-breeding wrinkle-seeded pea plants, you would get more round-seeded pea plants in the next generation than if you crossed all the round-seeded pea plants from the F1 generation with true-breeding wrinkle-seeded pea plants.
(b) The reason you do not see wrinkle-seeded pea plants in the F1 generation is because the round-seeded pea plants used to create the F1 generation were not true-breeding strains.
(c) The gene for round-seeded pea plants is on a different chromosome from the gene for wrinkle-seeded pea plants, which is why you get 25% wrinkle-seeded pea plants in the F2 generation.
(d) If you crossed the round-seeded pea plants from the F2 generation with the wrinkle-seeded pea plants from the F2 generation, you should get 100% round-seeded pea plants.

Front 29

19-43 Which of the following reasons was essential for Mendel to disprove the theory of blended inheritance?

Back 29

(d) The traits that Mendel examined involved an allele that was dominant and an allele that was recessive.

Hint 29

(a) The traits that Mendel examined all involved genes that did not display linkage.
(b) The traits that Mendel examined all involved the reproductive structures of the pea plant.
(c) Mendel pioneered techniques permitting the fusion of male and female gametes from the same plant to produce a zygote.
(d) The traits that Mendel examined involved an allele that was dominant and an allele that was recessive.

Front 30

19-44 Which of the following reasons was essential for Mendel’s law of independent assortment?

Back 30

(a) All the traits that Mendel examined involved genes that did not display linkage.

Hint 30

(a) All the traits that Mendel examined involved genes that did not display linkage.
(b) Several of the phenotypes that Mendel examined involved color.
(c) Mendel observed chromosomal segregation in pea-plant cells.
(d) Mendel carried out his experiments on plants and not on fungi.

Front 31

19-53 Loss-of-function mutations ________________________.

Back 31

(d) are usually recessive.

Hint 31

(a) cause the production of proteins that are active in inappropriate circumstances.
(b) will usually show a phenotype when heterozygous.
(c) are only present in a population at barely detectable levels.
(d) are usually recessive.

Front 32

19-58 Haplotype blocks can be seen in humans because _______.

Back 32

(b) modern humans descended from a relatively small population of about 10,000 individuals that existed about two thousand generations ago.

Hint 32

(a) disease genes are found in haplotype blocks.
(b) modern humans descended from a relatively small population of about 10,000 individuals that existed about two thousand generations ago.
(c) some of our human ancestors interbred with Neanderthals.
(d) new mutations cannot be introduced into existing haplotype blocks.

Front 33

19-60 The single-nucleotide polymorphisms found in the human population __________________.

Back 33

(c) can be linked into haplotype blocks.

Hint 33

(a) are important for genetic mapping because they represent mutations in genes important for human disease.
(b) are rarely found among blood relatives.
(c) can be linked into haplotype blocks.
(d) arose mainly during the past 10,000 years.

Front 34

19-61 Which of the following statements about genome-wide association studies (GWAS) is false?

Back 34

(d) Studies using GWAS only examine SNPs that occur very rarely (<0.001%) in the population, as those SNPs are most likely to cause disease.

Hint 34

(a) GWAS use SNPs to compare populations of people with disease and people without disease to look for SNPs more likely to be present in those with disease.
(b) GWAS can be used even if more than one gene can cause the disease of interest.
(c) Sometimes GWAS will identify SNPs that are associated with a disease but these SNPs do not affect the gene product of the gene that causes the disease.
(d) Studies using GWAS only examine SNPs that occur very rarely (<0.001%) in the population, as those SNPs are most likely to cause disease.

Front 35

19-62 Finding co-inheritance of a SNP variant and a disease tells scientists that ____________________.

Back 35

(c) a gene important for causing the disease is linked to the SNP.

Hint 35

(a) everybody who carries this SNP will get the disease.
(b) sequences within the SNP cause the disease.
(c) a gene important for causing the disease is linked to the SNP.
(d) SNPs on other chromosomes will not be co-inherited with the disease.