Meiosis

Vocabulary Homologous Chromosomes – Refers to chromosomes that each have a corresponding chromosome from the opposite-sex parent

Diploid vs. Haploid Diploid - a cell containing both sets of homologous chromosomes Diploid means “2 sets” Chromosome number shown as 2N

Diploid vs. Haploid Haploid - a cell with only 1 set of homologous chromosomes Haploid means “1 set” Chromosome number shown as N

Tetrad When each pair of homologous chromosomes have replicated/duplicated, they form tetrads (4 chromatids)

Interphase DNA replication- during “S” phase

Meiosis Making of haploid gametes egg, pollen, sperm In humans = 23 chromosomes

Prophase I 1. Prophase I Homologous chromosomes pair up, forming tetrads Tetrads

Crossing Over Happens during tetrad formation There is an exchange of genes or alleles Produces new combinations of alleles

Metaphase I 2. Metaphase I Chromosomes are lined up at the center of the cell Spindle fibers attach to chromosomes at the centromeres

Anaphase I 3. Anaphase I  Spindle fibers pull homologous chromosomes to opposite ends

Telophase I & Cytokinesis 4. Telophase I and Cytokinesis Nuclear membranes form Cells separate into two haploid (N) cells Which picture is cytokinesis? Which picture is telophase I?

Prophase II Chromosomes form

Metaphase II Chromosomes are lined up at the center of the cell Spindle fibers attach to chromosomes at the centromeres

Anaphase II Sister chromatids separate and move toward opposite ends of cell

Telophase II & Cytokinesis Results in 4 haploid (N) daughter cells

The End Result THE RESULTS Each daughter cell is genetically different from the others Male haploid gametes = sperm   Female = 1 egg (oocyte) & 3 polar bodies

What are the steps of meiosis? Rewatch Meiosis Video