11 4 Meiosis Chromosome Number Humans have 46

11 -4 Meiosis

Chromosome Number Humans have 46 chromosomes 23 from Mom 23 from Dad _______ 46 Homologous Chromosomes l Homologous = each of the 23 chromosomes from one parent has a matching pair of 23 from the other parent

Diploid l Every cell has homologous pair of chromosomes l Diploid number = “Two sets” l Represented by 2 N l In humans 2 N = 46 l Every cell in your body is diploid, except your gametes

Haploid l Gametes have only one set of chromosomes l They are Haploid = “one set” l Haploid is represented by N l In humans N = 23 l How do haploid gametes get made from diploid cells?

Meiosis l Meiosis the process of making gametes (sex cells) l In humans one cell with 46 chromosomes gets changed into 4 cells with 23 chromosomes

Meiosis l Meiosis is made up of 2 parts l Meiosis II l

Meiosis I Basically the same a Mitosis – first thing that happens is the chromosomes replicate l The chromosomes separate and the cell splits forming two daughter cells l Each cell containing one complete set of chromosomes and are both diploid=2 N=46 chromosomes forming tetrads l

Tetrads l 4 chromatids joined together l Crossing over = when the chromosomes in the tetrad exchange sections of DNA

Meiosis II l Both cells divide again but this time the chromosomes do not replicate l result = 4 daughter cells are all haploid = N = 23 chromosomes

Start with one cell 46 46 23 End up with 4 sex cells 23 23

Mitosis l How your body makes more body cells l Start with one cell and end up with two cells that are identical.

Starts with 1 cell 2 n (46) End up with 2 identical cells 2 n (46)