Chapter 19
Meiosis is a highly specialized cell division in which several events occur in a precisely defined order. Please order the meiotic events listed below. 1. loss of cohesins near centromeres 2. chromatid pairing 3. chromosome condensation 4. chromosome replication 5. degradation of cohesins bound to chromosome arms 6. formation of chiasmata (chiasmata = plural of chiasma) 7. homolog pairing 8. alignment of chromosomes at the metaphase plate
4, 2, 7, 6, 3, 8, 5, 1
A diploid cell containing 32 chromosomes will make a haploid cell containing ___ chromosomes. (a) 8 (b) 16 (c) 30 (d) 64
b
After the first meiotic cell division ________________________. (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.
b
A single nondisjunction event during meiosis ___________________. (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.
d
Do you agree or disagree with the following statement? Explain your answer. A trait that is found at a low frequency in the population has to be a recessive trait
Disagree (The frequency of a trait in a population has nothing to do with its dominance or recessiveness. To test dominance or recessiveness, the segregation of this trait must be observed. For example, the defective version of the gene involved in Huntington's disease occurs at a relatively low frequency in the population but behaves in a dominant fashion to cause disease.)
Do you agree or disagree with the following statement? Explain your answer. If a diploid organism has 16 chromosomes (and thus 8 pairs of homologous chromosomes), that organism can produce only 28 genetically different gametes.
Disagree (There are two distinct mechanisms for genetic variation in gametes. One method, the reassortment of chromosomes during meiosis, would result in a diploid Page 38 of 50 organism with 16 chromosomes producing 28 genetically different gametes. However, a much greater number of genetically different gametes can be produced as a result of the recombination between chromosomes that occurs during every meiosis.)
T/F: The phenotype of an organism reflects all of the alleles carried by that individual.
False (The phenotype, or the observable traits, of an organism often does not fully reflect its genotype, or the catalog of all alleles in the chromosomes. The reason is that some alleles are dominant (call these A) and other alleles are recessive (a). An individual who is heterozygous (Aa) for a dominant allele will have the same phenotype as one who is homozygous (AA).)
During recombination ________________________. (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.
b
Haplotype blocks can be seen in humans because _______. (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.
b
If you crossed the round-seeded plants obtained in the F1 generation with a truebreeding strain of wrinkle-seeded plants, how many round-seeded plants would you expect to obtain in the next generation? (See Figure Q19-38.) (a) 25% (b) 50% (c) 75% (d) 100%
b
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. (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
b
The formation of a bivalent during meiosis ensures that _______. (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
b
Which of the following could be considered a true-breeding strain for the seedshape phenotype? (See Figure Q19-38.) (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
b
Which of the following statements is false? (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.
b
Finding co-inheritance of a SNP variant and a disease tells scientists that ____________________. (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
c
In the absence of recombination, how many genetically different types of gamete can an organism with five homologous chromosome pairs produce? (a) 5 (b) 10 (c) 32 (d) 64
c
Somatic cells ___________________________. (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.
c
The single-nucleotide polymorphisms found in the human population __________________. (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.
c
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.) (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.
c
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. (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.
a
During fertilization in humans, _______________________. (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.
a
If you crossed the round-seeded plants obtained in the F1 generation with a truebreeding strain of round-seeded plants, how many wrinkle-seeded plants would you expect to obtain in the next generation? (See Figure Q19-38.) (a) none (b) 25% (c) 75% (d) all
a
Which of the following reasons was essential for Mendel's law of independent assortment? (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.
a
Which of the following statements about meiosis is true? (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.
a
Which of the following statements about the benefits of sexual reproduction is false? (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
a
Which of the following statements about the experiment diagrammed in Figure Q19-38 is true? (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 roundseeded pea plants in the next generation than if you crossed all the roundseeded pea plants from the F1 generation with true-breeding wrinkleseeded 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.
a
Which of the following statements is true? (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
a
T/F: Somatic cells leave no progeny and thus, in an evolutionary sense, exist only to help create, sustain, and propagate the germ cells.
True
During sexual reproduction, novel mixtures of alleles are generated. This is because ______. (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.
d
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. (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
d
In some fungi, cell division during meiosis gives rise to an ordered spore sac containing a row of four haploid spores, as shown in Figure Q19-30A. The position of each spore within the sac reflects its relation to its neighbors; in other words, spores that result from the same meiosis II division are positioned next to each other. You notice that a strain of the fungus produced by crossing a darkcolored strain with a light-colored strain gives rise mostly to spore sacs as shown in Figure Q19-30B, with a few spore sacs like those in Figure Q19-30C. Indicate whether the following statements are correct. Explain your reasoning. Figure Q19-30 A. Meiosis I and meiosis II in the fungus occur in the reverse order from that which occurs in humans. B. Recombination in the fungus can occur during prophase I. C. Recombination in the fungus cannot occur during prophase II. D. The spore sacs in Figure Q19-30C result from recombination between the centromere and the gene responsible for spore color. E. Recombination has occurred between the gene responsible for spore color and the end of the chromosome arm.
A. Incorrect B. Correct C. Not a valid deduction D. Correct E. Incorrect
Indicate whether each of the following is true for meiosis, mitosis, both, or neither. A. formation of a bivalent B. genetically identical products C. condensation of chromosomes D. segregation of all paternal chromosomes to one cell E. involvement of DNA replication
A. meiosis B. mitosis C. both D. neither E. both
Which of the following does not describe a situation of asexual reproduction? (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.
c
Which of the following statements about the round-seeded pea plants obtained in the F2 generation is false? (See Figure Q19-38.) (a) These plants are phenotypically identical for seed shape. (b) Two-thirds of these plants are expected to be heterozygous for the seedshape 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.
c
Which of the following would not lead to aneuploidy during meiosis? (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)
c
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. (a) all (b) none (c) 1/16 (d) 1/256
c
Loss-of-function mutations ________________________. (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
d
Organisms that reproduce sexually ________________________. (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
d
Which of the following reasons was essential for Mendel to disprove the theory of blended inheritance? (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
d
Which of the following statements about Mendel's experiments is false? (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.
d
Which of the following statements about genome-wide association studies (GWAS) is false? (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.
d
Which of the following statements most correctly describes meiosis? (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.
d
To reproduce sexually, an organism must create haploid __________________ cells, or __________________, from diploid cells via a specialized cell division called __________________. During mating, the father's haploid cells, called __________________ in animals, fuse with the mother's haploid cells, called __________________. Cell fusion produces a diploid cell called a __________________, which undergoes many rounds of cell division to create the entire body of the new individual. The cells produced from the initial fusion event include __________________ cells that form most of the tissues of the body as well as the __________________-line cells that give rise to the next generation of progeny. allele germ pollen bivalent meiosis somatic eggs mitosis sperm gametes pedigree zygote
germ, gametes, meiosis, sperm, eggs, zygote, somatic, germ
Gregor Mendel studied pea plants and developed some very important ideas about how genes are inherited. These studies used plant strains that were true breeding and always produced progeny that had the same __________________ as the parent. These strains were true breeding because they were __________________ for the gene important for a specific trait. In other words, for these true-breeding strains, both chromosomes in the diploid pea plant carried the same __________________ of the gene. Mendel started out examining the inheritance of a single trait at a time, and then moved on to examining two traits at once in a __________________ cross. His studies examining the inheritance of two traits in one cross allowed him to discover what is now known as Mendel's law of __________________ assortment. Geneticists can study the inheritance of specific traits in humans by analyzing a __________________, which shows the phenotypes of different family members over several generations for a particular trait. allele genotype monohybrid chromosome heterozygous pedigree dependent homozygous phenotype dihybrid independent segregation
phenotype, homozygous, allele, dihybrid, independent, pedigree
Starting with a single diploid cell, mitosis produces [two/four] [identical/different] [haploid/diploid] cells, whereas meiosis yields [two/four] [identical/different] [haploid/diploid] cells. This is accomplished in meiosis because a single round of chromosome [replication/segregation] is followed by two sequential rounds of [replication/segregation]. Mitosis is more like meiosis [I/II] than meiosis [I/II]. In meiosis I, the kinetochores on sister chromatids behave [independently/coordinately] and thus attach to microtubules from the [same/opposite] spindle. The cohesin-mediated glue between [chromatids/homologs] is regulated differently near the centromeres than along the chromosome arms. Cohesion is lost first at the [centromeres/arms] to allow segregation of [chromatids/homologs] and is lost later at the [centromeres/arms] to trigger segregation of [chromatids/homologs].
two, identical, diploid, four, different, haploid, replication, segregation, II, I, same, chromatids, arms, homologs, centromeres, chromatids
