Meiosis IMeiosis I• Prophase I – homologous chromosomes form tetrads & crossing over occurs• Metaphase I – tetrads line up along the middle

• Anaphase I – homologous chromosomes separate• Telophase I – two nuclei form

• Cytokinesis I – cells separate

2N

N N

Meiosis IIMeiosis II• Prophase II – spindle forms, prepares for division

• DNA replication DOES NOT occur between Meiosis I & II

• Metaphase II – chromosomes align along the center• Anaphase II – sister chromatids separate

• Telophase II – nuclei reform; cytokinesis

N N

N N NN Looks A LOT like MITOSIS!

Meiosis SummaryMeiosis Summary Chromosome number is cut in half!Chromosome number is cut in half! Produces haploid gamete cells – egg and spermProduces haploid gamete cells – egg and sperm Tetrads form during Prophase ITetrads form during Prophase I

Crossing over occurs in tetrad formation – Crossing over occurs in tetrad formation – leads to increased genetic variationleads to increased genetic variation

Two cell divisions, but DNA does not replicate Two cell divisions, but DNA does not replicate between divisionsbetween divisions

Results in 4 sperm cells in men and 1 egg in Results in 4 sperm cells in men and 1 egg in womenwomen

Which chromosomes wind up in which sex Which chromosomes wind up in which sex cells? It’s random…due to independent cells? It’s random…due to independent assortment!!assortment!!