Concept 1: Sexually reproducing organisms make sex cells or gametes

Gametes serve two functions. They have the physiological capability to fuse with a gamete from the opposite sex and form a single cell (a zygote) that initiates the development of a new organism and the next generation. They also carry a complete set of genetic instructions that this new organism will need to grow, develop and complete its life cycle. Gametes are made from the cells of an organism through a special division process called meiosis (see other lessons). This cell division process allows the gametes to have half of the genetic material of the original cell and the somatic (or "body") cells (Fig. 1). The genetic material is packaged in structures called chromosomes and the chromosomes sorted in an orderly fashion to give each gamete the one set of genetic instructions. Offspring made from sexual reproduction will have two sets of genetic instructions, one delivered from the male gamete (pollen in plants, sperm in animals) and one from the female egg (called an egg or ova in both plants and animals) (Fig. 2).

Figure 1. Somatic and gametic plant cells. Somatic cells have two of each type of chromosome, gametes have one of each. In the somatic cell, the two matching chromosomes are shown next to each other for purposes of seeing matching chromosomes, though they would not organize themselves this nicely in a somatic cell. Some slight coloration difference in the bands on the matching chromosomes indicates the chromosomes can have exactly matching genes on it or can be alternative versions of the same gene. (Image by P. Hain)

Figure 2. The sex cells of an example plant, maize (or corn). Sex cells are made in specialized organs and carry genetic information to the next generation. The pollen is present in the tassels of corn at the top of the corn plant. The egg is part of the ears of corn. Corn has both the male and female sex cells in it, but this is not the case for all plants. (Image by P. Hain)