Aim: How does meiosis form the gametes?

Review: Meiosis = 2 Cell Divisions 1st Cell Division 2nd Cell Division 1 Diploid cell 4 Haploid Cells

Prior to Cell Division Prior to cell division (mitosis or meiosis) the cell’s chromosomes must replicate.

II. Stages of Meiosis I: From one cell *Prophase I – Homologous Chromosomes pair up & exchange information *Metaphase I – Homologous chromosomes line up in the middle. *Anaphase I – Homologous Chromosomes separate (pairs split up) *Telophase I & Cytokinesis: Two Haploid Cells Form (chromosomes are still doubled)  *How many cells produced after 1st MEIOTIC division? _____

Meiosis I

Crossing over – Prophase I: Synapsis – homologous chromosomes pair up Crossing over – chromosomes overlap and exchange of genes.

Crossing Over…… Allows for variety in the sex cells that creates variety in offspring. This is why we are all DIFFERENT!!!

IV. Stages of Meiosis II: begins with 2 haploid cells from Meiosis I. *Prophase II – doubled chromosomes (2 pairs of sister chromatids) *Metaphse II – pairs line up in middle again  *Anaphase II – Sister Chromatids separate *Telophase II – each of the two cells separate into two new cells *How many cells produced after 2nd MEIOTIC division? _____

Meiosis II

Movie

Mid-Summary: How are mitosis and meiosis different? What type of cells are produced by meiosis? What happens before cell division? How many cells are produced by meiotic cell division? Are they diploid or haploid? What is synapsis? What is crossing over?

*Production of gametes (sperm & egg) by meiotic cell division Gametogenesis *Gameto = gametes *Genesis = creation *Production of gametes (sperm & egg) by meiotic cell division

Creation of an ovum or egg cell by meiotic cell division in the ovary. Oogenesis: Creation of an ovum or egg cell by meiotic cell division in the ovary.

How many eggs are produced?

There is an unequal sharing of the cytoplasm RESULT = 1 egg & 3 non functional polar bodies

Egg vs. Polar Bodies: The egg is very large, has most of the cytoplasm, which provides nutrients for the offspring.

Creation of sperm cells by meiotic cell division in the testes. Spermatogenesis: Creation of sperm cells by meiotic cell division in the testes.

How many sperm are produced by spermatogenesis? 4 equal sized sperms with flagella for swimming.

Spermatogenesis vs. Oogenesis

What is essential for sexual reproduction? *Gametes must have: motility to be able to meet and unite (move). b. food to nourish the developing embryo

Differences between Sex Cells & Body Cells:

Cell division producing body cells Mitosis = My toes

What type of cell division produces sex cells? Meiosis x

Mitosis = CLONES Meiosis = VARIATION What do each lead to? Mitosis = CLONES Meiosis = VARIATION

Summary: What is gametogenesis? Where does gametogenesis happen? What type of cells are produced by gametogenesis? What are the two types of gametogenesis? How many eggs are produced? How many sperm are produced?

Mitosis vs. Meiosis Points of Comparison Mitosis Meiosis # of cell divisions Exchange of genetic material between chromosomes # of functioning cells produced from the original Genetic makeup of final cells produced Function of cells produced in multicellular organisms