Concepts to Consider: The first female black cat was homozygous dominant for the albinism gene. The second female black cat was heterozygous. The albino male was homozygous recessive. All the offspring from the first mating were heterozygous. In the second mating, the black offspring were heterozygous, while the albinos were all homozygous recessive.

Concepts to Consider: The main problem with living on land is desiccation. Many animals have a body covering or integument that limits water loss. In addition, an efficient excretory system and the location of the respiratory system deep within the body also limit water loss. Another problem associated with a terrestrial existence is the effects of gravity, since there is no water to buoy the bodies of terrestrial organisms. Some animals overcome this problem by having small bodies or having strong supporting structures such as exoskeletons or endoskeletons. A third problem with living on land is how to join sperm and eggs. This can be overcome by having internal fertilization (copulation). Finally, eggs that are released from terrestrial animals may desiccate if they are not protected. One means of protection is surrounding eggs with a tough covering that prevents water loss, or storing eggs inside the body of the mother, surrounded by the body fluids of the parent.

D

A