114 ■ CHAPTER 06 Cell Division
(^10) Scientists are able to isolate cells in various phases of the cell
cycle. During an experiment in which Dr. Patrick McGroyn is causing
cultured tumor cells to go through mitotic cell division, he isolates
a group of cells that contain one and a half times more DNA than
cells isolated in the G 1 phase have. What phase must these cells be
in? How do you know?
Tr y Something New
(^11) Domesticated sheep cells have a total of 54 chromosomes
(versus 46 chromosomes in human cells).
(a) How many separate DNA molecules are present in a sheep liver
cell at the end of the G 1 phase?
(b) How many separate DNA molecules are present in the daughter
cells after meiosis I in the ovary of the sheep?
(c) How many separate DNA molecules are present in the daughter
cells after meiosis II in the ovary of the sheep?
(^12) Biopsies from aggressive cancers often have cells that contain
several nuclei per cell when viewed through a microscope. Which
scenario could explain how such a multinucleated cell might have
come to be?
(a) The cell underwent repeated mitosis with simultaneous
cytokinesis.
(b) The cell had multiple S phases before it entered mitosis.
(c) The cell underwent repeated mitosis, but cytokinesis did not occur.
(d) The cell underwent repeated cytokinesis but no mitosis.
(e) The cell actually went through meiosis and not mitosis.
(^13) Describe the likely consequences of bypassing the G
1 and G 2
checkpoints in the cell cycle. Why do compounds like nonylphenol
lead to the multiplication of abnormal cells?
Leveling Up
(^14) What do you think? Cancer begins with a single cell that breaks
loose of normal restraints on cell division and starts dividing rapidly
to establish a colony of rogue cells. As cancer cells spread through
the body, they disrupt the normal functions of tissues and organs;
unchecked, cancer can cause death through failure of multiple organ
systems. Many cancers could be prevented by not smoking or chewing
tobacco, eating less meat and processed foods, eating more fruits
and vegetables, drinking alcohol only moderately if at all, exercising
regularly, and maintaining a healthy weight. Only 5–10 percent of
cancers are directly attributable to genetic causes.
A “sin tax” is a tax on a product or activity that has negative
effects on others, as a way to offset some of those effects. Common
targets of sin taxes are tobacco and alcohol because of their public
health costs. Proponents of a sin tax on tobacco argue that such a
tax would decrease the amount that people smoke (because of the
increased cost) and could also partially fund the costs of medical
care necessitated by increased rates of cancer and other diseases
caused by smoking. Critics point out that sin taxes have historically
(^4) Select 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.
(^5) 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
(^6) 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
(^7) Loss of cell cycle control may lead to
(a) pregnancy.
(b) cancer.
(c) fertilization.
(d) crossing-over of homologous chromosomes.
Challenge Yourself
(^8) Suppose a scientist has recently identified a new protein
that prevents a cell from entering mitosis if there are any signs of
DNA damage. This protein would be classified as a type of
protein.
(a) chromatid
(b) cell cycle checkpoint
(c) benign
(d) malignant
(e) angiogenesis
(^9) You’ve been reduced in size by a misfire from a “shrink-inator”
gun! You realize that you are inside a cell during prophase I of
meiosis. You see two linear molecules of DNA compacted and
attached to one another by a centromere. What exactly are you
looking at?
(a) a homologous pair of chromosomes
(b) sister chromatids
(c) the metaphase plate
(d) cell cycle checkpoints
(e) gametes