Meiosis How to make SEX cells!

What is Meiosis? Most living things have body cells and sex cells (sperm and eggs) Eggs are female sex cells Sperm are male sex cells Meiosis is a special cell division that results in sex cells

What’s the Big Picture? In meiosis, a cell divides twice making a total of how many cells? 4

What’s the Big Picture? 1st time, each chromosome in a pair move away from its partner, each chromosome goes to a different cell, sister chromatids stay joined together 2nd division – sister chromatids separate

Some Terms: Cells that have the normal number of chromosomes are called “Diploid” Cells that have ½ the normal number of chromosomes are called “Haploid” Meiosis results in 4 Haploid cells that are genetically different from each other (and remember the parent cell was diploid)

Some Terms: Cells have pairs of chromosomes each chromosome in a pair is “homologous” to the other (they are homologs). In meiosis the homologous chromosomes separate.

Interphase I DNA Replicates

PROPHASE 1 Nuclear membrane begins to break down Centrioles begin to move away from each other Homologous (matching) chromosomes come together to form “tetrads” (remember: each chromosome has 2 strands of sister chromatids – now looks like 4 strands)

Metaphase 1 Sister chromatids become attached to fibers Homologous chromosomes move to the center of the cell

Anaphase 1 Tetrads separate into double stranded chromosomes

Telophase 1 Cell membrane pinches cell into two Nuclear membrane does not reform

Interphase II DNA DOES NOT Replicate

Prophase II (2) Centrioles double and form fibers again

Metaphase II (2) Fibers connect chromatids and they line up at the middle

Anaphase II (2) Fibers pull each strand apart to opposite ends of the cell

Telophase II (2) Cells Divide – Now have 4 cells Each has ½ the # of Chromososmes (Haploid) Each is genetically different from the others Nuclear membrane reforms Cell pinches off

The Whole Thing Part 1…

The Whole Thing Part 2…