Semen is a fluid that carries sperm, or male reproductive cells, out of the body during ejaculation. The average amount of ...

For species that rely on sexual reproduction, including mice and men, offspring can only happen if sperm from the male fertilize eggs from the female. Even artificial fertilization techniques depend ...

For decades, sperm were thought to become fully active the moment they entered the female reproductive tract. New research suggests otherwise. A temperature-sensitive switch inside sperm cells may ...

Mice are the envy of the genetics world thanks to the ease with which these animals can be genetically altered by tinkering with cultured embryonic stem (ES) cells. When it comes to making straight ...