MEIOSISCh. 11-4

Bill Nye Meiosis Movie

I. General InfoA. Two types of body cells:

1. Somatic cellsa) 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 process1. 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 11-15 on pages 276 AND 277

II. Stages of meiosisA. 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 materialiv. Produces greater genetic variability.

DRAW FIG 11-16, pg 276

B. Metaphase 11. Homologous chromosomes line up in the middle of

the cell.

C. Anaphase 11. Homologous chromosomes are pulled to opposite

poles.

D. Telophase 1/Cytokinesis 12. Sometimes chromosomes start to disappear.3. There is no interphase, therefore no doubling of

the chromosomes.

E. Prophase 21. Nuclear membrane disappears.

F. Metaphase 21. Chromosomes line up in the middle perpendicular to

their position in metaphase 1G. Anaphase 2

1. Chromosomes are pulled to the poles.2. Each cell will have half as many chromosomes as the

original cellH. 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 II Metaphase II Anaphase II Telophase IIThe 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 11-17 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 11-17 on page 278

Review of Oogenesis

V. Mitosis/Meiosis Cycle

CENSORED

DRAW

Meiosis Square Dance