Some Vocab Diploid (2n): two sets of chromosomes – You are diploid ( 46 chromosomes) 1 set from mom 1 set from dad Haploid (n): one set of chromosomes – Reproductive cells are haploid (23 Chromosomes) Eggs Sperm

Some Vocab Homologous Chromosomes: two chromosomes with the same gene sequence as another, one from each parent.

What is Meiosis? Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half.

What is Meiosis? Meiosis involves two divisions ◦ Meiosis I ◦ Meiosis II

Meiosis I  Interphase I – DNA replicates  Prophase I – Crossing over occurs  Metaphase I – Chromosomes line up  Anaphase I – Chromosomes are pulled apart  Telophase I/Cytokinesis – Nuclear membranes forms. The cell separates into two cells.

What is Crossing Over? Crossing over is when two homologous chromosomes pair up and exchange segments of their genetic material. Crossing over results in genetic recombination. Crossing over is what makes every egg and sperm cell unique. Crossing over is why you are not exactly like your siblings.

Crossing Over

Meiosis I

Meiosis II Very similar to mitosis FINAL PRODUCT = 4 genetically different HAPLOID DAUGHTER CELLS

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells. Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells. Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells. Meiosis II

Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. Prophase IIMetaphase IIAnaphase IITelophase II The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells. Meiosis II

Gamete Formation Males In male animals, the haploid gametes produced in meiosis are called sperm. Females In female animals, one cell receives most of the cytoplasm and will become an egg cell. The other three cells produced are known as polar bodies and do not participate in reproduction.

Gamete Formation Males Spermatogenesis Females Oogenesis

MeiosisMitosis Purpose What kind of cells are produced? # of divisions required # of cells needed to begin # of daughter cells produced # of chromosomes in daughter cells (n/2n) # of chromosomes in daughter cells in humans Are the daughter cells identical to the parent cell? Does crossing over occur? To produce gametes (sex / gametic cells) Production of body cells (somatic cells) Half the number of the parent cell (n) The same number as the parent cell (2n) No No Yes Yes