MEIOSIS Making the sex cells Meiosis The process

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