Challenge Questions

27. 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?

28. 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.)

(a) Father and child

(b) Mother and child

(c) Two full siblings (offspring that have the same two biological parents)

(d) Half siblings (offspring that have only one biological parent in common)

(e) Uncle and niece

(f) Grandparent and grandchild

29. 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?

30. 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 encodes 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.

SUGGESTED READINGS]_

Hawley, R. S., and T. Arbel. 1993. Yeast genetics and the fall of the classical view of meiosis. Cell 72:301 - 303.

Contains information about where in meiosis crossing over takes place and the role of the synaptonemal complex in recombination.

Jarrell, K. F., D. P. Bayley, J. D. Correia, and N. A. Thomas. 1999. Recent excitement about Archaea. Bioscience 49:530- 541.

An excellent review of differences between eubacteria, archaea, and eukaryotes.

King, R. W., P. K. Jackson, and M. W. Kirschner. 1994. Mitosis in transition. Cell 79:563- 571. A good review of how the cell cycle is controlled.

Kirschner, M. 1992. The cell cycle then and now. Trends in Biochemical Sciences. 17:281 - 285.

A good review of the history of research into control of the cell cycle.

Koshland, D. 1994. Mitosis: back to basics. Cell 77:951 - 954.

Reviews research on mitosis and chromosome movement.

McIntosh, J. R., and M. P. Koonce. 1989. Mitosis. Science 246:622 - 628.

A review of the process of mitosis.

McIntosh, J. R., and K. L. McDonald. 1989. The mitotic spindle. Scientific American 261(4):48 - 56.

Review of the mitotic spindle. McIntosh, J. R., and C. M. Pfarr. 1991. Mini-review: mitotic motors. Journal of Cell Biology 115:577 - 583.

Considers some of the experimental evidence concerning the role of molecular motors in the organization of the spindle and in chromosome movement. McKim, K. S., and R. S. Hawley. 1995. Chromosomal control of meiotic cell division. Science 270:1595 - 1601.

Reviews evidence that chromosomes actively take part in their own movement and in controlling the cell cycle. Morgan, D. O. 1995. Principles of CDK regulation. Nature 34:131 -134.

An excellent short review of cell-cycle control. Nasmyth, K. 1999. Separating sister chromatids. Trends in Biochemical Sciences 24:98 - 103.

Considers the role of cohesion in the separation of sister chromatids.

Pennisi, E. 1998. Cell division gatekeepers identified. Science 279:477 - 478.

Short review of work on the role of kinetochores in chromosome separation.

Pluta, A. F., A. M. MacKay, A. M. Ainsztein, I. G. Goldberg, and W. C. Earnshaw. 1995. Centromere: the hub of chromosome activities. Science 270:1591 -1594.

An excellent review of centromere structure and function. Rothfield, L., S. Justice, and J. Garcia-Lara. 1999. Bacterial cell division. Annual Review of Genetics 33:423 - 428.

Comprehensive review of how bacterial cells divide. Uhlmann, F., F. Lottespeich, and K. Nasmyth. 1999. Sister-chromatid separation at anaphase onset is promoted by cleavage of the cohesion subunit Scc1. Nature 400:37- 42.

Report that cleavage of cohesion protein has a role in chromatid separation. Zickler, D., and N. Kleckner. 1999. Meiotic chromosomes: integrating structure and function. Annual Review of Genetics 33:603 - 754.

A review of chromosomes in meiosis, their structure and function.

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