372 Chapter 18
CritiCaL thinKing
- Normally you can’t inherit both copies of a homologous
chromosome from the same parent. Why? Assuming that
no crossing over has occurred, how likely is it that one of
your non-sex chromosomes is an exact copy of the same
chromosome your maternal grandmother had? Explain
your answer. - Suppose you have a way of measuring the amount
of DNA in a single cell during the cell cycle. You first
measure the amount during the G1 phase. At what points
during the remainder of the cycle would you predict
changes in the amount of DNA per cell? - Adam’s maternal and paternal chromosomes have
alternate forms of a gene that influences whether a
person is right-handed or left-handed. One form says
“right” and its partner says “left.” Visualize one of
Adam’s spermatogonia, in which chromosomes are being
duplicated prior to meiosis. Visualize what happens to the
chromosomes during anaphase I and II. (It might help to
use toothpicks as models of the sister chromatids of each
chromosome.) What fraction of Adam’s sperm will carry
the gene for right-handedness? For left-handedness?
In cancer, cells divide abnormally
because the usual controls over mitosis
are lost. Researchers working with can-
cerous cells have identified how nearly
600 different genes affect mitosis in
those cells. The next step is to discover
how changes in such “mitosis” genes
affect healthy cells. This information
may provide much better understanding of exactly how mitosis
goes awry as cancer gets started—knowledge that could help
lead to more effective treatment for some cancers.your Future
© Cengage Learning- Fresh out of college, Maria has her first job teaching
school. When she goes for a pre-employment chest X-ray
required by the school district, the technician places a
lead-lined apron over her abdomen but not over any other
part of Maria’s body. The apron prevents electromagnetic
radiation from penetrating into the protected body area.
What cells is the lead shield designed to protect, and why?
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