CHAPTER 19 SEX AND GENETICS 2009 Garland Science Publishing The Benefits of Sex 19 1 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 19 2 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 19 3 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 19 4 Somatic cells a are not necessary for sexual reproduction in all eucaryotic organisms b are used to produce germ line cells when organisms reach sexual maturity c leave no progeny d do not contain sex chromosomes 19 5 Which of the following statements about the benefits of sexual reproduction is false a b c d 19 6 Sexual reproduction permits enhanced survival because the gametes that carry alleles enhancing survival in harsh environments are used preferentially during fertilization Unicellular organisms that can undergo sexual reproduction have an increased ability to adapt to harsh environments Sexual reproduction reshuffles genes which is thought to help species survive in novel or varying environments Sexual reproduction can speed the elimination of deleterious alleles For each of the following sentences fill in the blanks with the best word or phrase selected from the list below Not all words or phrases will be used each word or phrase may be used more than once 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 bivalent eggs gametes germ meiosis mitosis pedigree pollen somatic sperm zygote 19 7 Why is sexual reproduction more beneficial to a species living in an unpredictable environment than to one living in a constant environment 19 8 Is the following statement true or false Explain Somatic cells leave no progeny and thus in an evolutionary sense exist only to help create sustain and propagate the germ cells 19 9 Sexual reproduction is a large drain on the limited resources of an individual Nonetheless sexual reproduction is common In fact to allow sexual reproduction organisms have evolved many elaborate anatomical structures cellular processes and chemical signals For example flowers exist entirely to further the goal of sexual reproduction and many plants have enlisted the help of bees and birds to aid in the dissemination of their germ cells Describe one reason why most multicellular organisms have evolved to reproduce sexually instead of relying solely on asexual reproduction Meiosis and Fertilization 19 10 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 19 11 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 19 12 For each of the following sentences choose one of the options enclosed in square brackets to make a correct statement 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 cohesinmediated 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 19 13 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 19 14 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 19 15 A diploid cell containing 32 chromosomes will make a haploid cell containing chromosomes a 8 b 16 c 30 d 64 19 16 Imagine a diploid sexually reproducing organism Diploidus sexualis that contains three pairs of chromosomes This organism is unusual in that no recombination between homologous chromosomes occurs during meiosis A Assuming that the chromosomes are distributed independently during meiosis how many different types of sperm or egg cells can a single individual of this species produce B What is the likelihood that two siblings of this species will be genetically identical You can assume that the homologous chromosomes of each parent are