Cell Division Meiosis

Relationship Between Meiosis and Genetics Meiosis results in egg (females) and sperm (males) cells. When egg and sperm combine a new human is formed. The egg carries the genes from mom and the sperm carries the genes from dad You are a combination of genes from your mom and your dad! Your eye color, hair color etc. all depends on which egg cell and sperm cells combine!

Let Us Review Mitosis Cellular division involving replication and division of chromosomes (DNA). New cell contains complete set of chromosomes. (Two copies of genetic info.) Results in DIPLOID cells (chromosomes occur in pairs)

Diploid Cells Chromosomes in early interphase (actually chromatin) Chromosomes after replication (ready for mitosis) Both are Diploid Homologous Pairs

Diploid Cells cont. All body cells are diploid. Sex cells: egg and sperm are the only haploid cells

Sex Cells Germ Cells Only contain one copy of genetic information Also know as Sex Cells Only contain one copy of genetic information Have one chromosome of each pair or half that of diploid cells. Haploid (N) state.

Why is Haploid Important? If diploid cells are fertilized… + 2N + 2N  4N Chromosome will keep doubling!!

Why is Haploid Important? If haploid cells are fertilized… + N + N  2N Like all cells of the body!!

Sexual Reproduction Reproductive process in which haploid sex cells (gametes) fuse to produce a diploid fertilized egg (zygote) + EGG SPERM Fertilized Egg (ZYGOTE) GAMETES

46 36 # of Chromosomes 23 23 18 18 HUMAN CAT Total Chromosomes in a diploid cell # of homologous pairs in a diploid cell Total chromosomes in haploid cell HUMAN 46 CAT 36 23 23 18 18

MEIOSIS Cell division that reduces the number of chromosomes in half Occurs in sex cells (germ cells: Egg and Sperm) Two Divisions MEIOSIS I MEIOSIS II Meiosis I Meiosis II

Prophase I Chromosomes form Nuclear membrane and nucleolus disappear Synapsis – homologous chromosomes pair up Crossing Over – exchange of DNA creating genetic variability

Metaphase I Homologous chromosomes line up at the equator

Anaphase I / Telophase I Homologous chromosomes separate and move to opposite poles Cells are still diploid TELOPHASE I: Cell membrane pinches in

Interphase???? There is NO interphase between Meiosis I and Meiosis II

Prophase II Cells are haploid. Cells get ready to divide again.

Metaphase II Chromosomes align at the equator Looks like mitosis

Anaphase II / Telophase II Sister chromatids move to opposite poles TELOPHASE II: Cell membrane pinches in Nuclear membrane reappears.

Resulting Sex Cells Four HAPLOID sex cells are produced.

MEIOSIS

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