Chapter 5 Study Questions

House cat cells have a total of 38 chromosomes (versus the human 46 chromosomes). How many separate DNA molecules are present in a cat skin cell toward the end of the (a) G0 phase; (b) G1 phase; (c) S phase; (d) G2 phase?

(a) 38, (b) 38, (c) 76, (d) 76.

Which of the following is not a contributor to genetic variation? (a) replication of sister chromatids (b) crossing-over of homologous chromosomes (c) random assortment of homologous chromosomes (d) fertilization

(a) replication of sister chromatids

Homologous chromosomes are: (a) are the same thing as sister chromatids. (b) are a pair of chromosomes of the same kind. (c) are identical copies of the same chromosome. (d) are always haploid.

(b) are a pair of chromosomes of the same kind.

Loss of cell cycle control may lead to (a) pregnancy. (b) cancer. (c) fertilization. (d) crossing-over of homologous chromosomes.

(b) cancer.

Sister chromatids (a) are the same thing as homologous chromosomes. (b) are a pair of chromosomes of the same kind. (c) are identical copies of the same chromosome, attached at the centromere. (d) are always haploid.

(c) are identical copies of the same chromosome, attached at the centromere.

How is the cell cycle controlled? (a) Completion of one phase triggers the start of the next phase. (b) A cell divides when it reaches a critical size. (c) A cell divides when it reaches a particular age. (d) Internal or external signals at specific checkpoints may stop the cycle or trigger the start of the next phase.

(d) Internal or external signals at specific checkpoints may stop the cycle or trigger the start of the next phase.

Place the following events of sexual reproduction in the correct order by numbering them from 1 to 5. ____ a. Separation of homologous chromosomes ____ b. Separation of sister chromatids ____ c. Mitosis within the zygote, leading to a multicellular organism ____ d. Cytokinesis, leading to four haploid daughter cells ____ e. Fusion of two gametes

1) a. Separation of homologous chromosomes 2) b. Separation of sister chromatids 3) d. Cytokinesis, leading to four haploid daughter cells 4) e. Fusion of two gametes 5) c. Mitosis within the zygote, leading to a multicellular organism

Circle the correct terms in the following sentences: (Mitosis, Meiosis) produces daughter cells with half the number of chromosomes that the parent cell has. Cell division in prokaryotes is called (mitosis, binary fission). Meiosis I separates (sister chromatids, homologous chromosomes); meiosis II separates (sister chromatids, homologous chromosomes) into separate daughter cells.

Meiosis; binary fission; homologous chromosomes; sister chromatids

What is the difference between mitosis and cytokinesis?

Mitosis separates sister chromatids to opposite poles of the cell; cytokinesis divides the parent cell into two daughter cells.

Describe the likely consequences of bypassing the G1 and G2 checkpoints in the cell cycle. Why do compounds like nonylphenol lead to the multiplication of abnormal cells?

The G1 checkpoint ensures that the cell is ready to divide—for example, that it is large enough and has enough energy to produce two normal daughter cells. The G2 checkpoint ensures that the cell's DNA has been replicated and packed into pairs of sister chromatids. Bypassing the G1 checkpoint could allow cells to divide before they're ready; bypassing the G2 checkpoint could lead to the production of daughter cells with defective chromosomes.

The consequences of mitosis are easy to see during childhood, when an individual is growing rapidly, but examples of mitosis in adult life are less conspicuous. Nonetheless, you can probably find visible evidence of mitosis in progress on your own body right now. What examples can you suggest?

Wound healing is the most visible example of mitosis in progress. Peeling skin following a sunburn and the growth of hair, fingernails, and toenails are additional examples, although in these cases the replicating cells are beneath the surface of the skin.