MEIOSIS

I. General Info A. Your body makes two types of cells: 1. Somatic cells a) Contain 46 chromosomes (23 from Mom and 23 from Dad) b) They are diploid (2N) (they have two sets of chromosomes) c) Made by mitosis d) Examples: Liver, eye, brain, skin, etc. 2. Reproductive cells a) Contain 23 chromosomes b) They are haploid (1N) c) Made by meiosis d) Examples: Sperm and egg (called gametes)

Bill Nye Meiosis Movie

II. Meiosis and Gametes A. Gametes must be made by a special type of cell division called meiosis. 1.Males Produce Sperm a. haploid b. each sperm cell can be involved in reproduction 2. Females Produce Eggs a. haploid b. cell divisions are uneven c. only one cell receives most of cytoplasm d. other cells are called polar bodies

B. Meiosis occurs in two divisions 1. Meiosis 1 2. Meiosis 2

III. Meiosis 1 A.Prophase 1 1.Same as mitosis prophase, except chromosomes duplicated during interphase are visible and pair up with each other.

2. Crossing over takes place a.When the chromosomes crossover they break at that point b.Then they rejoin on opposite chromosomes and there has been an exchange of genetic material c.Produces genetic diversity

B. Metaphase 1 1. Chromosomes line up in the middle of the cell. C. Anaphase 1 1. Chromosomes are pulled to the poles. D. Telophase 1/Cytokinesis 1 1. Cytoplasm divides and two new cells are formed  Unlike in MITOSIS, cells do not go into Interphase after cytokinesis 1, so chromosomes are not duplicated.

IV. Meiosis 2 PMAT occurs again with one difference: 1.Chromosomes get separated into two chromatids during anaphase 2.

V.Meiosis Summary A. Two cells are formed in Meiosis 1. B. Both cells from Meiosis 1 form two cells in Meiosis 2 resulting in the production of 4 new cells. C. Each cell has half the number of chromosomes as the original cell.  From one human cell w/46 chromosomes, meiosis produces four gametes w/23 chromosomes each.

Overview of Meiosis

VI. Mitosis/Meiosis Cycle Adult (2N) Eggs (N) Sperm (N) Zygote (2N) Meiosis Mitosis Fertilization A. Fertilization occurs when sperm and egg join to form one big cell called a zygote

Animal Cell Meiosis

Meiosis Square Dance