MEIOSIS Ch. 11-4

Bill Nye Meiosis Movie

I. General Info A. Two types of body cells: 1. Somatic cells a) Any non-sex cell (e.g. liver, eye, heart, brain) b) Diploid (2N) = contains 2 sets of chromosomes c) Made by mitosis 2. Germ cells (reproductive) a) Called gametes (sperm or eggs) b) Haploid (1N) = contain 1 set of chromosomes c) Must be made by a special type of cell division called meiosis.

B. Meiosis is a reduction division process 1. The chromosomes are reduced to half the original number (e.g. in humans it goes from 46 to 23) 2. Meiosis has one DNA (chromosome) duplication and two division cycles.  Draw Figure on pages 276 AND 277

II. Stages of meiosis A. Prophase 1 1. Different from mitosis: a) Homologous chromosomes move close together and connect at the centromere.

b) Crossing over takes place: i.On homologous chromosomes. ii.When the chromosomes crossover they break at that point. iii.Then they rejoin on opposite chromosomes and there has been an exchange of genetic material iv.Produces greater genetic variability. DRAW FIG 11-16, pg 276

B. Metaphase 1 1. Homologous chromosomes line up in the middle of the cell. C. Anaphase 1 1. Homologous chromosomes are pulled to opposite poles. D. Telophase 1/Cytokinesis 1 1. Sometimes chromosomes start to disappear. 2. There is no interphase, therefore no doubling of the chromosomes.

E. Prophase 2 1. Nuclear membrane disappears. F.Metaphase 2 1. Chromosomes line up in the middle perpendicular to their position in metaphase 1 G.Anaphase 2 1. Chromosomes are pulled to the poles. 2. Each cell will have half as many chromosomes as the original cell H.Telophase 2/Cytokinesis 2 1. From one original cell, 4 daughter gametes are formed with half the chromosomes as the original cell.

Meiosis I

Meiosis II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells.

Meiosis Overview

III. Sperm formation: “Spermatogenesis” A. In males: 1. Process of meiosis results in 4 haploid sperm cells.  Draw “In Males” Figure on page 278

IV. Ovum (egg) formation:“Oogenesis” A. In female gametes the process is the same except at: 1. Telophase 1 - one cell gets most of the cytoplasm. a) Results in secondary egg and one polar body. 2. Telophase 2 - same thing occurs B. This leaves three non-functioning polar bodies and one large ovum.  Draw “In Females” Figure on page 278

Review of Oogenesis

V. Mitosis/Meiosis Cycle CENSORED DRAW

Meiosis Square Dance