Chapter Two: Chromosomes and Cellular Reproduction COMPREHENSION QUESTIONS

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  1. All organisms have the same universal genetic system. What are the implications of this universal genetic system?
  2. Why are the viruses that infect mammalian cells useful for studying the genetics of mammals?

*3.    List three fundamental events that must take place in cell reproduction.

  1. Outline the process by which prokaryotic cells reproduce.
  2. Name three essential structural elements of a functional eukaryotic chromosome and describe their functions.

*6.    Sketch and label four different types of chromosomes based on the position of the centromere.

  1. List the stages of interphase and the major events that take place in each.

*8.    List the stages of mitosis and the major events that take place in each.

*9.    What are the genetically important results of the cell cycle?

  1. Why are the two cells produced by the cell cycle genetically identical?
  2. What are checkpoints? What two general classes of compounds regulate progression through the cell cycles?
  3. What are the stages of meiosis and what major events take place in each?

*13.  What are the major results of meiosis?

  1. What two processes unique to meiosis are responsible for genetic variation? At what point in meiosis do these processes take place?

*15.  List similarities and differences between mitosis and meiosis. Which differences do you think are most important and why?

  1. Outline the process by which male gametes are produced in plants. Outline the process of female gamete formation in plants.
  2. Outline the process of spermatogenesis in animals. Outline the process of oogenesis in animals.
  3. A certain species has three pairs of chromosomes: an acrocentric pair, a metacentric pair, and a submetacentric pair. Draw a cell of this species as it would appear in metaphase of mitosis.
  4. A biologist examines a series of cells and counts 160 cells in interphase, 20 cells in prophase, 6 cells in prometaphase, 2 cells in metaphase, 7 cells in anaphase, and 5 cells in telophase. If the complete cell cycle requires 24 hours, what is the average duration of M phase in these cells? Of metaphase?

*20.  A cell in G1 of interphase has 12 chromosomes. How many chromosomes and DNA molecules will be found per cell when this original cell progresses to the following stages?

*21.  All of the following cells, shown in various stages of mitosis and meiosis, come from the same rare species of plant. What is the diploid number of chromosomes in this plant? Give the names of each stage of mitosis or meiosis shown.

  1. A cell has 1x amount of DNA in G1 of interphase. How much DNA (in multiples or fractions of x) will be present per cell at the following stages?
  2. A cell in prophase II of meiosis contains 12 chromosomes. How many chromosomes would be present in a cell from the same organism if it were in prophase of mitosis? Prophase I of meiosis?

*24.  The fruit fly Drosophila melanogaster has four pairs of chromosomes, whereas the house fly Musca domestica has six pairs of chromosomes. Other things being equal, in which species would you expect to see more genetic variation among the progeny of a cross? Explain your answer.

*25.  A cell has two pairs of submetacentric chromosomes, which we will call chromosomes Ia, Ib, IIa, and IIb (chromosomes Ia and Ib are homologs, and chromosomes IIa and IIb are homologs). Allele M is located on the long arm of chromosome Ia and allele m is located at the same position on chromosome Ib. Allele P is located on the short arm of chromosome Ia and allele p is located at the same position on chromosome Ib. Allele R is located on chromosome IIa and allele r is located at the same position on chromosome IIb.

  1. A horse has 64 chromosomes and a donkey has 62 chromosomes. A cross between a female horse and a male donkey produces a mule, which is usually sterile. How many chromosomes does a mule have? Can you think of any reasons for the fact that most mules are sterile?

CHALLENGE QUESTIONS

  1. Suppose that life exists elsewhere in the universe. All life must contain some type of genetic information, but alien genomes might not consist of nucleic acids and have the same features as those found in the genomes of life on Earth. What do you think might be the common features of all genomes, no matter where they exist?
  2. On average, what proportion of the genome in the following pairs of humans would be exactly the same if no crossing over occurred? (For the purposes of this question only, we will ignore the special case of the X and Y sex chromosomes and assume that all genes are located on nonsex chromosomes.)
  3. Females bees are diploid and male bees are haploid. The haploid males produce sperm and can successfully mate with diploid females. Fertilized eggs develop into females and unfertilized eggs develop into males. How do you think the process of sperm production in male bees differs from sperm production in other animals?
  4. Rec8 is a protein that is found in yeast chromosome arms and centromeres. Rec8 persists throughout meiosis I but breaks down at anaphase II. When the gene that codes for Rec8 is deleted, sister chromatids separate in anaphase I.
    • (a) From these observations, propose a mechanism for the role of Rec8 in meiosis that helps to explain why sister chromatids normally separate in anaphase II but not anaphase I.
    • (b) Make a prediction about the presence or absence of Rec8 during the various stages of mitosis
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