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)
Chromosomes after replication (ready for mitosis) Chromosomes in early interphase (actually chromatin) Homologous Pairs Diploid Cells Both are Diploid
Diploid Cells cont. • All body cells are diploid. • Sex cells: egg and sperm are the only haploid cells
Sex Cells • Germ Cells • 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.
# of Chromosomes 23 23 18 18
+ 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
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 ANAPHASE 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 ANAPHASE 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.