Many living things have 2 parents. Each parent gives their offspring half of the recipes it takes to make the offspring. “Offspring” is a fancy way of saying “babies” because we don’t usually think of coral, or seeds, or mushrooms as babies.

The recipes for a living thing, whether it is a bacterium, pine tree, or giant squid are in its DNA. The DNA comes from their parents. Humans have about 24,000 recipes or genes. We actually get two copies of each recipe, one from our mom and one from our dad. For example, you have a recipe for the pigment that gives your hair its color. You got one copy of that recipe from your mom and one copy of the recipe from your mom. Maybe the recipes were the same. Both the recipes from my parents were for brown hair. Someone else may have a copy for brown hair from one parent and a copy for red or blonde hair from another parent. Another person may have two copies of a black hair recipe. There are lots of possibilities.

The sperm is the cell that has a whole set of recipes from the father. He may pass along the recipe for hair color that he got from his mother or the one he got from his father. It’s random for each sperm. It’s also random for the other 24,000 recipes that each sperm will have. Egg cells also have one copy of each of the 24,000 genes.

Sperm cells can usually move. In most animals, the sperm swim with a tail (flagellum). They may swim in the sea, or a river, or in the reproductive system of a female. In plants, the sperm are in pollen. They might be carried by the wind or by a pollinator, like a hummingbird, bat, or bee. Egg cells give off chemicals that attract swimming sperm. If the sperm reach an egg, the tail drops off and they deliver the DNA to the egg. The egg already has all of the other things a cell needs.

Sperm are produced by males and by living things that are both male and female. Eggs are produced by females and by living things that are both male and female.

Why do you think sperm are so much smaller than eggs?

Sperm are the cells that contribute the father’s genetic information to the baby. The egg has the mother’s genetic information. Only one sperm fertilizes one egg, but there are usually 100s of millions of sperm that will try to fertilize the egg.

A sperm cell looks a little like a tadpole, it has a head which has its genetic information and a tail which lets it swim towards the egg. Once the sperm reaches the egg, it releases molecules that break up the cells surrounding the egg and eventually the head of the sperm fuses with the egg. Once it fuses, the genetic information of the sperm enters the egg and the fertilized cell will eventually grow into a full-grown organism.

Sperm are the smallest cells in the human body, whereas eggs are the largest cells, which is why the sperm dumps its genetic information into the egg and not the other way around. The general concept of sperm fertilizing eggs is present in many multicellular organisms, including animals, algae, fungi, and plants.

Sperm are small, mobile cells that fuse with larger, less mobile cells called eggs to produce a new living cell called a zygote. This zygote then grows into an adult animal or plant.