Life cycle of a bacterium (a prokaryote) showing asexual reproduction.	Life cycle of a flowering plant (a multicellular eukaryote) showing sexual reproduction.

In addition, the female parent donates the all organelles for the new organism. Since some organelles have their own Instruction Books, this -- very rarely -- produces traits that are received only from the mother. This exception to the normal rule of some traits from each parent is called maternal inheritance.

The reproductive situation for eukaryotes is more complicated. For starters, unicellular eukaryotes can reproduce either asexually (by dividing their single cell) or sexually (by mating with another of their kind). For example, yeast and algae switch between sexual and asexual reproduction depending on outside conditions. All multicellular eukaryotes are capable of sexual reproduction, and nearly all of them reproduce exclusively by it. A few, though, can reproduce asexually by dividing in two.

Since unicellular eukaryotes have only one cell and one set of Instruction Books to copy, each asexual division produces two independent organisms. While this is very similar to the way prokaryotes reproduce, all eukaryotes -- even unicellular ones -- need to do a bit more work to insure that their daughter cells get a copy of each of their chromosomes. (Prokaryotes are a bit sloppy about copying their Instruction Books, so sometimes their offspring lose Instructions carried on plasmids.) Eukaryotic cell division for growth of the organism is called mitosis to distinguish it from prokaryotic reproduction and from eukaryotic sexual reproduction.

All multicellular eukaryotes grow by mitosis. This is how a multicellular organism gets its many cells: it starts as a single cell that divides into two cells, then four cells and -- after many divisions -- into thousands or billions of cells, depending on the organism. All the cells produced during growth make up a single organism and all act together.

All multicellular life can reproduce sexually. As multicellular organisms grow and mature, some of their cells differentiate into sexual organs (gonads). Gonads produce special cells, called gametes, whose purpose is to combine with other gametes during mating to produce a new organism. No other cells in most multicellular living things can reproduce or survive independently. Gametes and the cells in the gonads that produce them are sometimes called an organism's germ line or germ plasm. ("Germ" is an old term for what we call Instruction Books.) The other cells -- the ones that can't reproduce -- are called somatic or body cells.

There's one small exception to the two-parent rule of sexual reproduction: a few kinds of multicellular life are capable of reproducing by themselves through parthenogenesis. In parthenogenesis, a female organism produces gametes that combine with others of her own gametes, and thus she acts as both parents to her offspring. Although this looks a lot like asexual reproduction, parthanogenesis uses the machinery of sexual reproduction. Some plants take this idea further. They produce both male and female gametes on separate flowers. These plants can either reproduce either with themselves or with other plants.

Some multicellular eukaryotes are capable of reproducing asexually. This unusual ability is largely restricted to plants and fungi, but a few simple animals manage it as well. Certain plants (spider plants and some grasses) will take root any place a stem touches the ground. If the stem connecting the two rooted parts breaks, the two halves will survive as separate plants. Earthworms can similarly survive being cut in two. Some microscopic (but still multicellular) animals sprout miniature copies of themselves, which simply divide off when they're big enough to survive on their own.

Since the cells of all organisms undergo division by asexual reproduction -- either for growth or for reproduction of the whole organism -- we'll discuss it before sexual reproduction.