Analyzing semen under a microscope, she looks for the following characteristics: at least 15 million or more sperm cells, at least 40% of those cells moving and at least 4% of them shaped normally.

Just because a sperm is a strong swimmer doesn't necessarily mean it has the right amount of DNA, Dr. Lisa Lee told Newsweek.

While using a light microscope to study sperm formation in wasps, Henking noticed that some wasp sperm cells had 12 chromosomes, while others had only 11 chromosomes. Also, during his observation ...