1. Vocabulary Important Info Headings
MEIOSIS IN 123 & 125
Vocabulary
Important Info
Headings

2. Mitosis: Meiosis: formation of somatic cells (body cells)
At the end of mitosis each of the 2 daughter cells has 46 chromosomes
These are your body cells; cells that make up tissues, organs, etc.
Meiosis:
Formation of sex cells called gametes.
At the end of meiosis each of the 4 daughter cells has 23 chromosomes.
They contain 1/2 the # of chromosomes

3. Meiosis Gametes are special cells used in sexual reproduction.
These cells contain 1/2 the normal # of chromosomes than the regular body cells.
When the sperm and egg unite the zygote will contain the normal # of chromosomes for that organism

4. Egg(23 chrom) + sperm(23 chrom) = zygote(46 chrom)
CELL DIVISION
CELL TYPE
# OF DAUGHTER CELLS
# OF CHROMO-SOMES
Mitosis
Somatic (body) 2 46
Diploid
Meiosis
Gamete
(sex) 4 23
Haploid
Meiosis reduces the number of chromosomes to ½ the # in body cells.
This is called the haploid number (46  23)
Reductive division is necessary so that when reproduction occurs =
Zygote contains the necessary 46 chromosomes.
Egg(23 chrom) + sperm(23 chrom) = zygote(46 chrom)

5. 2 Divisions of Meiosis There are 2 divisions of meiosis:
Meiosis I and Meiosis II.
Must be in order to end up with:
Each sex cells containing: = 23 chromosomes

6. Meiosis I
During the first meiotic division, chromosomes are replicated.
Prophase I
chromatin makes a copy of itself
begins to coil up

7. This forms a tetrad (meaning 4).
2. Metaphase I
homologous pairs of chromosomes line up together at the middle of the cell.
This forms a tetrad (meaning 4).
*Homologous chromosomes are paired chromosomes.
*Each contains genes for the same trait.

8. 3. Anaphase I-
Homologous chromosomes that form each tetrad separate and move to opposite ends.
The centromeres (hold chromatids together) do not split.

9. 4. Telophase I-
Spindle fibers disappears
Cell divides by:
Cytokinesis (a cleavage forms)

10. Meiosis II During the second meiotic division NOTHING is replicated.
Prophase II-
centriole doubles
spindle forms

11. 2. Metaphase II-
chromosomes line up at the middle

12. 3. Anaphase II-
Individual chromatids move to opposite ends

13. 4. Telophase II-
2 daughter cells divide into 4 new daughter cells
Each new daughter cell has 23 chromosomes.
This is ½ the # of the original parent cell.

14. Where Does Meiosis Occur?
Testes of the male:
Called Spermatogenesis.
4 sperm are produced.
Ovaries of the female:
Called Oogenesis.
4 cells are produced
Only 1 becomes an egg used for reproduction!!!
Other 3 dissolve

15. Meiosis I in Motion
I- chromatin  chromosome & nuclear membrane disappears
P1- centrioles move to opp. Sides of cell
M1- 4 chromosomes line up in middle (tetrad)
A1- chromosomes (intact) pulled to opp. Sides by spindle fibers
T1- cell spits forming 2 new cells

16. Meiosis II in Motion P2- centrioles move to opp. Sides of each cell
M2- 2 chromosomes line up in middle
A2- chromatids pulled apart by spindle fibers
T2- cell spits forming 4 daughter cells that contain haploid set of chromosomes