Quick review: identify this stage of the diploid cell cycle.

Quick review: identify this stage of the diploid cell cycle.

Quick review: identify this stage of the diploid cell cycle.

Quick review: identify this stage of the diploid cell cycle.

Quick review: identify this stage of the diploid cell cycle.

Quick review: identify this stage of the diploid cell cycle.

• Defined: Process where the chromosome number is reduced by half

• Gametes created (egg & sperm)

• End Result: Four Haploid Cells

• Same process–G1: Growth

–S: Chromatin duplicated

–G2: Growth

Synthesis (S stage)

Chromatin strands duplicated

• Similar as mitosis, except…• Two Events:

– 1) Synapsis: Pairing of homologous chromosomes

– Dad’s #1 chromosome pairs with Mom’s #1, etc…– The four paired chromatids equals a TETRAD

– 2) Crossing Over: Exchange of genes

Mom 1

Dad 1

Early Prophase

dad

mom

mom

dad

dad

mom

Chromosomes form

Nucleus dissolves

Synapsis

dad

mom

mom

dad

dad

mom

Spindle fibers pull homologous chromosomes together

tetrad

tetrad

tetrad

• Homologous chromosomes (tetrads) align along cell equator

dad

dad

dad

mom

mom

mom

• Homologous chromosomes are pulled apart to opposite ends

–Tetrads separatedmom

dad

momdad

dadmom

• Cytokinesis divides the cells• Each cell contains 1 of the

homologous chromosomes

mom

dadm

om

dad

dadm

om

• Same as mitosis

• Note: No new DNA was created (no 2nd interphase)

mom

dadm

om

dad

dadm

om

• Remaining chromosomes are aligned at cell equator

mom

dadm

om

dad

dadm

om

• Sister chromatids are pulled to opposite ends

• Cytokinesis divides the cells• Nucleus reforms on the four new cells• Chromatids uncoil• End Result: Four haploid cells

• Defined: Production of sperm cells

• Location: male testes• Makes final changes

to sperm cell• Four haploid sperm

cells at a time

Meiosis 1

Meiosis 2

Spermatogenesis

spermatogonium

• Defined: Production of the egg cell (ovum)– In female ovaries

• During meiosis I: Cytoplasm distributed unequally

• After meiosis II:

– 1 cell matures

– 3 “Polar Bodies” dissolve

Meiosis 1

Meiosis 2

Oogenesis

oocyte

• Division of somatic cells

• Ex: Blood cells, skin cells, nerve cells…

• End Result: 2 Diploid Cells

• Importance: Replaces aging cells

• Importance: Form of asexual reproduction

• Division of gametes

• Ex: Sperm and Egg cells

• End Result: 4 Haploid cells

• Importance: Reduces the gamete chromosome number by half

Kobe Kuiz

1) Name three ways that meiosis and mitosis differ.

2) Pick a stage of meiosis…any stage. Describe what happens in it.

3) What type of cells does meiosis create?

4) What are homologous chromosomes?

5) When do homologous chromosomes move to opposite ends of the cell?

6) When do chromatids move to opposite ends of the cell?

7) Why is no DNA created in meiosis 2?

8) How does meiosis differ in males vs. females?