MitosisCell division/ cell productionWhat kind of cells?Nerve, skin, epithelial, etc.- somaticSame / all the time Mitosis is reproduction in which cells

produce identical replicasOrganic growth of tissues, fibers, and

membranes

MEIOSIS

MeiosisMeiosis occurs in sexual reproduction

when a diploid germ cell produces four haploid daughter cells that can mature to become gametes (sperm or egg).

MeiosisThe genetic code of a human contains 46

chromosomes

Half of this number is in egg and sperm

Divided twice which turns out 4 cells (gametes)

Each of these will have only half of the number of chromosomes; but each will contain genetic info from each parent

Mitosis Meiosis

Number of divisions 1 2

Number of daughter cells 2 4

Genetically identical? Yes No

Chromosome # Same as parent Half of parent

Where Somatic cells Sex cells

When Throughout life At sexual maturity

Role Growth and repair Sexual reproduction

http://www.youtube.com/watch?v=D1_-mQS_FZ0&feature=related

Interphase I Cells undergo a round of DNA replication

forming duplicate chromosomesEach chromosome has two sister chromatids

held together by a centromere

Prophase IChromosomes coil up and

spindle formsEach chromosome pairs

with its corresponding homologous chromosome to form a tetrad

Crossing over may occur when chromatids exchange genetic material

Crossing over results in new combinations of alleles on a chromosome

Crossing Over

Metaphase I The centromere of

each chromosome becomes attached to a spindle fiber

Spindle fibers pull the tetrads to the equator of the spindle

Homologous chromosomes are lined up side by side as tetrads

Anaphase IThe fibers pull the

homologous chromosomes toward opposite end of the cell

Centromeres do not split

This ensures that each new cell will receive only one chromosome from each homologous pair

Telophase IThe spindle breaks

down and the chromosomes uncoil

The cytoplasm divides to yield two new cells

Each cell has half the genetic info of the original cell because it has only one homologous chromosome from each pair

Prophase II Meiosis I results in two haploid (N) daughter

cells, with half the number of chromosomes as the original cell

A spindle forms in each of the two new cells and the fibers attach to the chromosomes

Metaphase II The chromosomes

line up in a similar way to the metaphase stage of mitosis

The chromosomes are pulled to the center of the cell and line up randomly at the equator

Anaphase IIThe centromere of

each chromosome splits

The sister chromatids separate and move toward opposite ends of the cells

Telophase IINuclei re-formThe spindles breakdownThe cytoplasm divides

Meiosis IIMeiosis II results in four haploid (N) daughter

cells.Each haploid cell contains one chromosome from

each homologous pairHaploid cells will become gametes transmitting

genes to off spring

What Meiosis is About

Meiosis allows the creation of unique individuals through sexual reproduction.