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Meiosis

I). Meiosis basics

A).  Cell division that results in the creation of haploid gametes.

Diploid (2n):

Haploid (1n):

B).    Meiosis occurs during:

Gametogenesis: formation of gametes

http://www.bio.miami.edu/dana/104/104F02_4.html

spermatogenesis: 

oogenesis:

C). Terms:

somatic cells

Somatic cells are 2n. They contain a set of chromosomes one from the mother one from the father

homologues.

One pair of chromosomes

gene:

allele:

Gametes

Each contain only one member of each homologue pair.

When fertilization occurs the normal diploid number is returned.

http://www.ck12.org/flexr/chapter/2412/

D). Meiosis involves 2 separate cell divisions and produces 4 daughter cells

II). Stages of Meiosis

A).  Meiosis I (Duplication & Crossing over)

1). Interphase I

• DNA replicates

2). Prophase I

	Chromatids coil and condense
	Synapsis and crossing over occurs

Synapsis:

 

i). STEP i:     Homologues chromosomes  form tetrads

ii). STEP ii:   The arms chromosomes wrap around each other.

iii). STEP iii: The arms of the homologues crossover.

Advantage:  increased variability in the offspring.

3). Metaphase I

Line up on the equator.

4). Anaphase I

Separate but centromeres do not break.

5). Telophase I

 

a).  Daughter cells have haploid chromosome number because they do not have homologues chromosomes. 

They have either the maternal or the paternal part of the pair.  It varies for each pair.

 

b).  Daughter cells have diploid DNA material because the sister or duplicate chromatids are still attached.

 

B).  Meiosis II

http://www.biologycorner.com/APbiology/inheritance/10-1_meiosis.html

1). Prophase II

chromosomes do not duplicate

2). Metaphase II

line up on the equator

3). Anaphase II

4). Telophase II & cytokinesis

The nuclear envelope begins to form and cytokinesis occurs.

5). 4 haploid daughter cells

4 sperm:

or

3 polar bodies & 1 ovum