Meiosis Making the sex cells

Meiosis The process of nuclear division that produces sex cells is called meiosis. Meiosis is also called sexual reproduction since it makes the sperm cells in males and egg cells in females. (Mitosis is called asexual reproduction since it makes body cells). The sex cells are called gametes The male gamete is the sperm The female gamete is the egg (ovum/ova)

Meiosis In sexual reproduction, a new organism is produced when sex cells from two parents combine. How many chromosomes are in a human body cell? There are 46 chromosomes in a human body cell A human sex cell has 23 chromosomes. Why do they have only half the number of chromosomes? Because the sperm’s 23 chromosomes are going to combine with the egg’s 23 chromosomes to make the first body cell of the baby with 46 chromosomes.

Meiosis In body cells (somatic cells), chromosomes are found in matching pairs. If each human cell has 46 chromosomes, how many matching pairs will form? There will be 23 pairs of chromosomes. The pairs form because the chromosomes are alike (not identical, though).

Meiosis A cell that has 2 of every kind of chromosome is said to be diploid. Human body cells are diploid (each of their 46 chromosomes can be matched up into 23 pairs). Sex cells have half the number of chromosomes as body cells so they do not have matching pairs. A sex cell with just one chromosome from each pair is called haploid.

Sexual Reproduction Sexual reproduction starts with the formation of the sex cells and ends when one sex cell joins with another and a new organism is begun. The joining of an egg and a sperm is called fertilization. The cell that forms in fertilization is called a zygote. If an egg with 23 chromosomes joins with a sperm that has 23 chromosomes, how many chromosomes will the zygote have? The zygote will have 46 chromosomes A zygote then begins to undergo mitosis and the organism develops