Cell Division

Meiosis

Relationship Between Meiosis and Genetics

• Meiosis results in egg (females) and sperm (males) cells.

• When egg and sperm combine a new human is formed.

• The egg carries the genes from mom and the sperm carries the genes from dad

• You are a combination of genes from your mom and your dad!

• Your eye color, hair color etc. all depends on which egg cell and sperm cells combine!

Let Us Review Mitosis

• Cellular division involving replication and division of chromosomes (DNA).

• New cell contains complete set of chromosomes. (Two copies of genetic info.)

• Results in DIPLOID cells (chromosomes occur in pairs)

Diploid Cells

• Chromosomes after replication (ready for mitosis)

• Chromosomes in early interphase (actually chromatin)

Both are Diploid

Homologous Pairs

Diploid Cells cont.

• All body cells are diploid.

• Sex cells: egg and sperm are the only haploid cells

Sex Cells

• Germ Cells

– Also know as Sex Cells

• Only contain one copy of genetic information

• Have one chromosome of each pair or half that of diploid cells.

• Haploid (N) state.

Why is Haploid Important?

• If diploid cells are fertilized…

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Chromosome will keep doubling!!

2N + 2N 4N

Why is Haploid Important?

• If haploid cells are fertilized…

+

Like all cells of the body!!

N + N 2N

Sexual Reproduction

• Reproductive process in which haploid sex cells (gametes) fuse to produce a diploid fertilized egg (zygote)

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EGG SPERM Fertilized Egg

GAMETES

(ZYGOTE)

# of Chromosomes

Total Chromosomes

in a diploid cell

# of homologous

pairs in a diploid cell

Total chromosomes

in haploid cell

HUMAN 46CAT 36

23 23

1818

MEIOSIS

• Cell division that reduces the number of chromosomes in half

• Occurs in sex cells (germ cells: Egg and Sperm)

• Two Divisions– MEIOSIS I

– MEIOSIS II

Meiosis I

Meiosis II

Prophase I

• Chromosomes form• Nuclear membrane and

nucleolus disappear• Synapsis – homologous

chromosomes pair up• Crossing Over –

exchange of DNA creating genetic variability

Metaphase I

• Homologous chromosomes line up at the equator

Anaphase I / Telophase I

ANAPHASE I:

• Homologous chromosomes separate and move to opposite poles

• Cells are still diploid

TELOPHASE I:

• Cell membrane pinches in

Interphase????

Prophase II

• Cells are haploid.

• Cells get ready to divide again.

Metaphase II

• Chromosomes align at the equator

• Looks like mitosis

Anaphase II / Telophase II

ANAPHASE II:

• Sister chromatids move to opposite poles

TELOPHASE II:• Cell membrane pinches in

• Nuclear membrane reappears.

Resulting Sex Cells

• Four HAPLOID sex cells are produced.

MEIOSIS

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