1. How do the following situations or practices disrupt Hardy-Weinberg equilibrium?

     a. Couples who find out they are heterozygotes for the same illness decide to not have children together.

     b. Several dozen young adults in a large Midwestern city discover they are half-siblings. Each was conceived by artificial insemination, with sperm from the same donor.

     c. Members of a very close-knit Amish community are forbidden to marry outside the community.

     d. A new viral illness kills only people who have a certain blood type.

2. A thin-shelled crab can more readily move to escape a predator than can a thick-shelled crab, but it is more vulnerable to predators that drill through the shell. As a result of these opposing forces, shell thickness for many types of crabs has remained within a narrow range, over a long time. What type of natural selection does crab shell thickness illustrate?

3. Which factors contributing to evolution discussed in this chapter do the following science fiction film plots illustrate?

     a. In When Worlds Collide, the earth is about to be destroyed. One hundred people, chosen for their intelligence and fertility, leave to colonize a new planet.

     b. In The Time Machine, set in the distant future on earth, one group of people is forced to live on the planet’s surface and another group is forced to live in caves. After many years, they look and behave differently. The Morlocks, who live belowground, have dark skin, dark hair and are very aggressive, whereas the Eloi, who live aboveground, are blond, fair-skinned, and meek.

     c. In Children of the Damned, genetically identical beings from another planet impregnate all the women in a small town.

     d. In The War of the Worlds, Martians cannot survive on earth because they are vulnerable to infection by terrestrial microbes. behave differently. The Morlocks, who live belowground, have dark skin, dark hair and are very aggressive, whereas the Eloi, who lived aboveground, are blond, fair-skinned, and meek.

4. How is in vitro evolution similar to the Foundry Cove experiments discussed in Investigating Life 14.1?

Additional Questions and Terms

1. In gene therapy, a functioning gene replaces a defective gene. In what part of an organism would this have to be performed to influence evolution? Why?

2. Use the information in this chapter to explain the following:

3. When the American Kennel Club formed more than a century ago, its stated goal was “to do everything to advance the study, breeding, exhibiting, running and maintenance of purity of thoroughbred dogs.” How is the idea of controlled breeding to emphasize certain traits genetically unwise?