Set up Cornell Notes on pg. 77 Topic: 6.2 Process of Meiosis Essential Questions: 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) 6.2 Process of Meiosis 2.1 Atoms, Ions, and Molecules On Pg. 66 please make a detailed flow map of the phases of meiosis Must have color Picture Description (in your own words)

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

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

Homologous Chromosomes Homologous chromosomes are very similar to one another Carry the same genes One from Mom One from Dad

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

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.

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

Meiosis has 2 cell divisions Results in 4 unique haploid cells 1 2

Meiosis I occurs after DNA has been replicated in the S stage Meiosis I divides homologous chromosomes in four phases.

Dad Prophase I: The nuclear membrane breaks down duplicated chromosomes condense homologous chromosomes pair up Appear to pair up precisely, gene for gene Mom Dad Mom

Dad Mom Metaphase I: Homologous chromosomes randomly align along the cell equator (middle) Which creates genetic diversity Each side of equator has chromosomes from both parents Dad Mom

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

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

Anaphase I: The homologous pairs separate from each other and move to opposite sides of the cell Sister chromatids remain attached

Telophase I: Nuclear membrane forms The cell undergoes cytokinesis Each cell has a unique combination of 23 duplicated chromosomes from both parents

Meiosis II divides sister chromatids in four phases DNA is not replicated between meiosis I and meiosis II

Prophase II: The nuclear membrane breaks down The centrosomes move to opposite sides of the cell and spindle fibers form

Metaphase II: Spindle fibers align the chromosomes along the cell equator

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

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

Meiosis I Meiosis II

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.

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.

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

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

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

Meiosis #: Name of Phase Meiosis I Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II Meiosis #: Name of Phase PICTURE Short description of what is happening in this phase