Chapter 19: Sexual Reproduction and the Power of Genetics

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 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.

You conduct a genetic screen on peas and isolate four mutant strains, each carry ing a recessive mutation that causes the production of red peas (instead of the wild- type green peas). To test whether these mutations are in the same gene, you perform complementation tests between the four different true- breeding strains. The results from these complementation tests are shown in Table#19-33

Given this data, how many genes do these four alleles represent? a. 1 b. 2 c. 3 d. 4

Figure 19-24 diagrams one of Mendel's experiments using the round and wrinkled seed traits. A

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? a. none b. 25% c. 75% d. all

Figure 19-24 diagrams one of Mendel's experiments using the round and wrinkled seed traits. B

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? a. 25% b. 50% c. 75% d. 100%

Figure 19-24 diagrams one of Mendel's experiments using the round and wrinkled seed traits. B

Which of the following could be considered a true-breeding strain for the seed-shape phenotype? 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

Figure 19-24 diagrams one of Mendel's experiments using the round and wrinkled seed traits. - A

Which of the following statements about the experiment diagrammed in Figure 19-28 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 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.

Figure 19-24 diagrams one of Mendel's experiments using the round and wrinkled seed traits. C

Which of the following statements about the round- seeded pea plants obtained in the F2 generation is FALSE? 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.

30. 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. All the traits that Mendel examined involved genes that did not display linkage.

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. Another name for the fertilized egg cell is the zygote.

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

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

Both budding yeast and the bacteria E. coli are unicellular life forms. 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. Unlike E. coli, budding yeast can alternate between a diploid state and a haploid state.

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

A diploid cell containing 32 chromosomes will make a haploid cell containing __________ chromosomes. a. 8 b. 16 c. 30 d. 64

b. 16

Which of the following statements about conditional alleles is FALSE? a. Conditional alleles allow for the study of lethal mutations in haploid organisms. b. Conditional alleles are only defective under high temperature conditions. c. Conditional alleles can be used to study tissue-specific gene function in diploid organisms. d. Conditional alleles behave like the wild-type allele under permissive conditions.

b. Conditional alleles are only defective under high temperature conditions.

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

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

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

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. chiasmata hold chromosomes together.

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 2,000 generations ago. c. human germ cells do not undergo recombination. d. new mutations cannot be introduced into existing haplotype blocks.

b. modern humans descended from a relatively small population of about 10,000 individuals that existed about 2,000 generations ago.

condensation of chromosomes

both meiosis and mitosis

involvement of DNA replication

both meiosis and mitosis

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. 1/16

In the absence of recombination, how many genetically different types of gametes can an organism with five homologous chromosome pairs produce? a. 5 b. 10 c. 32 d. 64

c. 32

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

Finding co- inheritance of an SNP variant and a disease tells scientists that a. every body 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. a gene important for causing the disease is linked to the SNP.

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 non-homologous 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. a reciprocal rearrangement of parts between non-homologous chromosomes (for example, the left arm of Chromosome 2 exchanging places with the right arm of Chromosome 3)

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. can be linked into haplotype blocks.

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. leave no progeny.

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 in de pen dent 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. using in vitro fertilization to combine a sperm and an egg to create an embryo

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. All traits that Mendel studied were recessive.

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. Meiosis involves a single round of DNA replication followed by two successive cell divisions.

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

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

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. 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.

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 pre sent in a population at barely detectable levels. d. are usually recessive.

d. are usually recessive.

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

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

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 result in the production of two normal gametes if it occurs during meiosis II.

d. will result in the production of two normal gametes if it occurs during meiosis II.

formation of a bivalent

meiosis

genetically identical products

mitosis

segregation of a all parental chromosomes to one cell

neither meiosis and mitosis