Problem 31

Background and context

Sexual reproduction is the mixing of genetic material from two individuals to produce genetically unique offspring.

Sexual reproduction may mean the joining of sperm and eggs within animals’ bodies or it may mean the release of sperm and eggs into the environment. An individual may be one sex or both; it may start as one sex and switch during its life, or it may stay male or female.

Sexual reproduction starts with the combination of a sperm and an egg in a process called fertilization. This can occur either outside the body or inside the female. Both methods have advantages and disadvantages. Once fertilized, the eggs can develop inside the female or outside. If the egg develops outside the body, it usually has a protective covering over it. Animal anatomy evolved various ways to fertilize, hold, or expel the egg. The method of fertilization varies among animals. Some species release the egg and sperm into the environment, some species retain the egg and receive the sperm into the female body and then expel the developing embryo covered with a shell, while still other species retain the developing offspring through the gestation period.