Meiosis The formation of gametes sex cells Some

Meiosis The formation of gametes (sex cells)

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

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 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

Crossing Over

Crossing Over

Meiosis I

Meiosis I

Meiosis I

Meiosis I

Meiosis I

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

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

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

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

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

Gamete Formation Males Females • In male animals, the haploid • In female animals, one cell receives gametes produced in meiosis most of the are called sperm. 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

Meiosis Mitosis Purpose To produce gametes (sex / gametic cells) Production of body cells (somatic cells) # of divisions required 2 1 1 1 4 2 What kind of cells are produced? # of cells needed to begin # of daughter cells produced # of chromosomes in daughter cells (n/2 n) # of chromosomes in daughter cells in humans Half the number of the The same number as parent cell (n) the parent cell (2 n) 23 46 Are the daughter cells identical to the parent cell? No Yes Does crossing over Yes No