Meiosis and Sexual Reproduction 10.1 Overview

What are homologous chromosomes?  Found in diploid cells only  Identical order of genes  Alleles (versions of genes) may vary

What is meiosis?  Chromosomal reduction—production of gametes  Two stages  Meiosis I  Meiosis II  Produces 4 daughter cells  daughter cells are NOT identical—see why on the next slide  haploid cells  Compare to mitosis

Why are daughter cells not identical?  Meiosis increases genetic variation  Two ways  Crossing over  Synapse  Bivalent  During prophase I  Independent assortment  During metaphase I

Why is there sexual reproduction?  Genetic variation  Disease resistance  Why create gametes?  Diploid number would double every generation otherwise  Haploid gametes maintain diploid number

What else increases genetic variation?  Fertilization  Haploid gamete + haploid gamete = diploid zygote

Meiosis and Sexual Reproduction 10.2 Meiosis I

What happens in Meiosis I?  Reduction of chromosomal number  2n (1 cell)  1n (2 cells)  Crossing over  Independent assortment  Same stages as mitosis  Key point: separation of HOMOLOGOUS CHROMOSOMES, not sister chromatids

Note: At Anaphase I, the cells are now HAPLOID

Meiosis and Sexual Reproduction 10.3 Meiosis II

What happens in Meiosis II?  Just before: interkinesis (like interphase)  Separation of sister chromatids  Basically the same as mitosis except cells are haploid, not diploid

What happens in Meiosis II?

Meiosis and Sexual Reproduction 10.4 Comparisons and gamete production

How do mitosis and meiosis compare?

What is spermatogenesis?  Production of spermatids  Spermiogenesis is conversion to sperm cells

What is oogenesis?  Manufacture of egg cells  Polar bodies  Meiosis II delayed until fertilization