6.2 Process of Meiosis Set up Cornell Notes on pg. 77•Topic: 6.2 Process of Meiosis

•Essential Questions:

1.On Pg. 66 please make a detailed flow map of the phases of meiosis I and II•Must have color•Picture•Description (in your own words)

2.1 Atoms, Ions, and Molecules

1. On Pg. 66 please make a detailed flow map of the phases of meiosis

• Must have color• Picture• Description (in your own words)

6.2 Process of Meiosis

6.2 Process of Meiosis

KEY CONCEPT During meiosis, diploid cells undergo two cell divisions that result in haploid cells.

6.2 Process of Meiosis

• Germ cells (46) develop into gametes through meiosis• Meiosis reduces chromosome number (46 to 23) and

creates genetic diversity. • All organisms that reproduce sexually must undergo

meiosis

6.2 Process of Meiosis

Homologous Chromosomes

• Homologous chromosomes are very similar to one another

• Carry the same genes

• One from Mom

• One from Dad

6.2 Process of Meiosis

Crossing over during meiosis increases genetic diversity. • Crossing over is the exchange of chromosome

segments between homologous chromosomes.– occurs during prophase I of meiosis I– results in new combinations of genes

6.2 Process of Meiosis

• Chromosomes contain many genes.

– The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over.

6.2 Process of Meiosis

• Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage.

6.2 Process of Meiosis • Meiosis has 2 cell divisions

• Results in 4 unique haploid cells

1

2

6.2 Process of Meiosis

• Meiosis I • occurs after DNA has been replicated in the S stage

• Meiosis I divides homologous chromosomes in four phases.

6.2 Process of Meiosis

MomDad

Mom Dad

• Prophase I:

• The nuclear membrane breaks down

• duplicated chromosomes condense

• homologous chromosomes pair up

• Appear to pair up precisely, gene for gene

6.2 Process of Meiosis

• Metaphase I:

• Homologous chromosomes randomly align along the cell equator (middle)

• Which creates genetic diversity

• Each side of equator has chromosomes from both parents

MomDad

Mom Dad

6.2 Process of Meiosis

1. If, during metaphase I, all 23 maternal chromosomes lined up on the same side of the cell, would genetic diversity increase?

6.2 Process of Meiosis

1. Genetic diversity would not increase because the maternal and paternal chromosomes would not become arranged in new combinations.

6.2 Process of Meiosis

• Anaphase I:

• The homologous pairs separate from each other and move to opposite sides of the cell

• Sister chromatids remain attached

6.2 Process of Meiosis

• Telophase I:

• Nuclear membrane forms

• The cell undergoes cytokinesis

• Each cell has a unique combination of 23 duplicated chromosomes from both parents

6.2 Process of Meiosis

6.2 Process of Meiosis

Meiosis II • divides sister chromatids in four

phases

• DNA is not replicated between meiosis I and meiosis II

6.2 Process of Meiosis

• Prophase II:

• The nuclear membrane breaks down

• The centrosomes move to opposite sides of the cell and spindle fibers form

6.2 Process of Meiosis

• Metaphase II:

• Spindle fibers align the chromosomes along the cell equator

6.2 Process of Meiosis

• Anaphase II:

• The sister chromatids are pulled apart from each other and move to opposite sides of the cell.

6.2 Process of Meiosis

• Telophase II:

• The nuclear membranes form again around the chromosomes

• spindle fibers break

• cell undergoes cytokinesis

RESULT: 4 unique haploid cells, with a combination of chromosomes from both the mother and father

6.2 Process of Meiosis

6.2 Process of Meiosis

Meiosis I

Meiosis II

6.2 Process of Meiosis

• Meiosis differs from mitosis in significant ways.

– Meiosis has two cell divisions while mitosis has one.– In mitosis, homologous chromosomes never pair up.– Meiosis results in haploid cells; mitosis results in diploid

cells.

6.2 Process of Meiosis

Haploid cells develop into mature gametes.

• Gametogenesis (gamet-o-genesis) is the production of gametes from haploid cells.

– Includes both meiosis and other changes that produce a mature cell

– differs between females and males.

6.2 Process of Meiosis

Sperm:–Much smaller than the egg–Main contribution to embryo is DNA–Must be able to move- has a tail that allows it to swim to egg

• During gametogenesis:• DNA tightly packed• Much cytoplasm is lost,

forming a head• Forms a flagellum • Forms neck region-

packed with mitochondria that drives cell

• Addition of new proteins

6.2 Process of Meiosis

Eggs:–Eggs contribute DNA, cytoplasm, and organelles to an embryo.–During meiosis, the egg gets most of the contents; the other cells form polar bodies.

– Begins before birth– Not finished until egg is

fertilized– Only one of the 4 haploid

cells actually becomes an egg

– The other 3 become polar bodies- only DNA inside

6.2 Process of Meiosis

• Sexual reproduction creates unique combination of genes.– random fertilization of gametes

• Unique phenotypes may give a reproductive advantage to some organisms.

Sperm= 8 million different combinations

Egg= 8 million different combinations

Any sperm can fertilize any egg= 64 TRILLION possible combinations

6.2 Process of Meiosis

Meiosis #: Name of Phase

PICTURE

Short description of what is happening in this phase

Meiosis I •Prophase I•Metaphase I•Anaphase I•Telophase I

Meiosis II•Prophase II•Metaphase II•Anaphase II•Telophase II