11-4 Meiosis Pg. 275

A. Purpose of Meiosis 1. Make reproductive cells (sex cells). 2. Reduces chromosome # in half.

B. Chromosome Number 1. The same type of chromosomes (male + female).

B. Chromosome Number 2. 2 sets of homologous chromosomes in cells = DIPLOID. 2N=46

B. Chromosome Number 3. Reproductive cells contain one set of chromosomes = HAPLOID N=23

Practice!!! 1. Human cells- 2n=46 2. Human Cells- n= 23 Haploid or Diploid? 2. Human Cells- n= 23 Haploid or Diploid?

C. Phases of Meiosis

INTERPHASE Chromosomes not visible. Chromosomes are replicated.

Meiosis I: PROPHASE I Centrioles move apart. Homologous chromosomes line up (tetrad). Crossing over occurs. Diploid

CROSSING OVER

Meiosis I: METAPHASE I Centrioles attach to spindle fiber. Tetrads line up in the middle. Diploid

Meiosis I: ANAPHASE I Homologous chromosomes separate to opposite poles. Diploid

Meiosis I: TELOPHASE I The chromosomes uncoil, cytoplasm divide and spindle disappears. Contains half the genetic material of original cell. Diploid

Meiosis II: Prophase II Centrioles move to opposite poles. Spindle fibers begin to form. Nucleolus disappears and nuclear envelope breaks apart. Haploid

Meiosis II: METAPHASE II Chromosomes line up in the middle. Spindle fibers attach to the centromeres. Haploid

Meiosis II: ANAPHASE II Chromosomes split into sister chromatids. Haploid

Meiosis II: TELOPHASE II Chromosomes move to opposite poles A nuclear envelope and membrane begins to re-form. Cytoplasm begins to separate Haploid

Remember PMAT P= Pairs M= Middle A= Apart T= Two