MeiosisCell division process whereby the number of chromosomes in a diploid cell is reduced by half through the separation of homologous chromosomes. This produces the gametes.

Why Meiosis?• Meiosis • To produce gametes (sex) cells• Egg and Sperm cells

Terms Review…

• Haploid: (n) having a single set of chromosomes in the cell. ex. Gametes; humans have 23 chromosomes in sex cells (egg and sperm cells)

• Diploid: (2n) having two sets of homologous chromosome in the cell. ex. Somatic (body) cells; humans have 23 pairs or 46 chromosomes in body cells

Human Karyotype with 23 pairs of homologous chromosomes for a diploid number of 46; 2n = 2(23) = 46

Terms Continued

• Homologous chromosomes – two sets of chromosome in a pair, with one set coming from a male parent and the other set coming from the female parent.

• Tetrad – pairing of homologous chromosomes during meiosis I, and such pairing has 4 (tetra) chromatids. These chromatids can then exchange genetic material.

• Crossing-over – process in which tetrad of homologous chromosomes exchange portions of their chromatids, and thus genetic material is exchanged; this occurs during Prophase I of meiosis.

• Gametes – sex cells; involved in sexual reproduction. Male gametes are called sperm cells and female gametes are called egg cells; sperm are produced in testes and egg are produced in ovaries by meiosis.

Section 11-4

Crossing-Over

Section 11-4

Crossing-Over

Section 11-4

Crossing-Over

Crossing Over

• What is happening?Exchange of genetic material between homologous chromosomes

• How does this affect the individual (offspring)? Creates genetic variation

Crossing Over

How does Meiosis Occur?

Meiosis Review

1. Is the beginning parent cell diploid or haploid (2n or n)?

2. Are the resulting daughter cells diploid or haploid (2n or n)?

More Meiosis Review

3. How many daughter cells are produced?

4.Are the resulting daughter cells different

from the parent cell?

More Meiosis Review

5. Are the resulting daughter cells different from each other?

7. How many chromosomes are in a human daughter cell?

6. How many chromosomes are in a human parent cell?

More Meiosis Review

8. What types of cells are produced by meiosis?

Fertilization

New Individual46

Mom

23

Dad

23

This is how new organisms are made!!

Let’s reviewMitosis & Meiosis

Mitosis vs. Meiosis  

   Event Mitosis Meiosis

Produces 4 cells

Produces 2 cells

New cells identical

New cells different

New cells have the same number of chromosomes as parent

New cells have fewer chromosomes than parent

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Mitosis vs. Meiosis  

   Event Mitosis Meiosis

Beginning cells diploid (2n)

Beginning cells haploid (n)

Ending cells diploid (2n)

Ending cells haploid (n)

Produces egg and sperm

Produces body cells

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