CHROMOSOME NUMBER & GAMETE FORMATION

CHROMOSOME NUMBER  organisms that reproduce sexually have a diploid number (2N) of chromosomes in each cell of their bodies  i.e. occur in pairs (1 chromosome from each parent)  each specie has its own diploid number March 4, 2016 OrganismDiploid no. (2N) Haploid No. (N) Humans46 Dogs/chickens78 Fruit fly8 Crayfish

Homologous Chromosomes homologous pair:  a pair of the same type of chromosomes containing the same sets of genes, originating from each parent  all cells have 2 complete sets of genes (double genes) for every trait March 4, 2016 humans:  have 23 pairs of homologous chromosomes mom ’ s dad ’ s eye colour gene hair colour gene

Fertilization: March 4, 2016 ovarian cell 2N = 46 testes cell 2N = 46 ovum 1N = 23 sperm 1N = 23 fertilization zygote 2N = 46 meiosis union of specialized egg & sperm to form a zygote (fertilized egg) mitosis 2N = 46 2N = 46 4N = 92

Fertilization gametes:  specialized sex cells  (i.e.) sperm or egg  contain ½ usual number of chromosomes  i.e. the haploid number (N)  contain only 1 chromosome from each homologous pair March 4, 2016 fertilization:  restores the diploid number in the zygote

Meiosis March 4, 2016 meiosis:  special cell division which reduces the number of chromosomes from diploid to haploid to form gametes  occurs only in the germinal cells of the testes & ovaries  involves 2 cell divisions: meiosis I reduction division diploid to haploid meiosis II like mitosis separates double- stranded chromosomes

Mitosis vs. Meiosis March 4, 2016 meiosis I meiosis II mitosis 46 meiosis diploid cells 4 haploid cells 1 diploid cell

Gamete Formation Spermatogenesis (males):  4 haploid sperm are formed  spermatogenesis continues throughout a male’s life  ~ 1000 sperm produced per minute March 4, 2016 single- stranded chromosomes double-stranded chromosomes single-stranded chromosomes chromosomes replicate 2N 1N

Gamete Formation Oogenesis (females):  1 haploid cell keeps most of the cytoplasm to become the egg (ovum)  the others become polar bodies & degenerate March 4, 2016 Note: Ovarian germ cells in female babies have all undergone meiosis I before birth. Meiosis II occurs after puberty, in 1 egg at a time at ovulation. OOGENESIS chromosomes replicate single- stranded chromosomes double-stranded chromosomes single-stranded chromosomes 2N 1N

Microscope Activity  Obtain a prepared slide of an onion root tip.  Using a microscope, locate and draw one cell in each of the following stages of mitosis… 1. interphase 2. prophase 3. metaphase 4. anaphase 5. telophase Mitosis Lab interphase metaphaseprophase telophase anaphase Set up your page like this…

Homework March 4, 2016 Study for Mitosis Quiz