Aim: How is chromosome number maintained in the species from generation to generation? Group Work: How many chromosomes are found in human cells? How many chromosomes pass from each parent to the child? Human chromosome number is 46 or 23 pairs.

Outcome of meiosis is that each cell gets half the number of chromosomes (one chromosome of each pair)

Oogenesis Egg formation takes place in the ovaries Egg contains the n number of chromosomes

Spermatogenesis Spermatogenesis — takes place in the testes. Each sperm cell contains the n number of chromosomes http://wps.aw.com/bc_martini_eap_4/0,11295,2680298-content,00.html

Comparison of (Meiosis) Spermatogenesis Oogenesis 1. production of sperm cell from puberty to the death of the male 2. produce 4 haploid sperm cells 3.very small cells with a tail 1. viable eggs are produced from puberty to menopause 2. produce 1 haploid egg cell and three smaller polar bodies 3. large cells

Mus musculus (house mouse) 40 Drosophila melanogaster (fruit fly) 8 Diploid numbers of some commonly studied organisms (as well as a few extreme examples) Homo sapiens (human) 46 Mus musculus (house mouse) 40 Drosophila melanogaster (fruit fly) 8 Caenorhabditis elegans (microscopic roundworm) 12 Saccharomyces cerevisiae (budding yeast) 32 Arabidopsis thaliana (plant in the mustard family) 10 Xenopus laevis (South African clawed frog) 36 Canis familiaris (domestic dog) 78 Gallus gallus (chicken) Zea mays (corn or maize) 20 Muntiacus reevesi (the Chinese muntjac, a deer) 23 Muntiacus muntjac (its Indian cousin) 6 Myrmecia pilosula (an ant) 2 Parascaris equorum var. univalens (parasitic roundworm) Cambarus clarkii (a crayfish) 200 Equisetum arvense (field horsetail, a plant) 216 All animals have a characteristic number of chromosomes in their body cells called the diploid (or 2n) number

Human Chromosomes

Human Homologous Chromosomes Human chromosomes are arranged by size the largest being chromosome number one.

Fertilization… restores the diploid number of chromosomes to the egg cell making it a zygote n + n = 2n