How does meiosis form the gametes?

Meiosis is 2 Cell Divisions 1st Cell Division 2nd Cell Division 4 Haploid Cells 1 Diploid cell

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

Stages of Meiosis Meiosis I - two cells Meiosis II – four cells with ½ the chromosome number Each meiotic cell division has the same stages (prophase, metaphase, anaphase, Telophase, cytokinesis)

Meiosis I

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

Meiosis II

Movie

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 cytoplasm 1 egg & 3 non functional polar bodies

Egg vs. Polar Bodies The egg is very large, has most of the cytoplasm, which will provide 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 food to nourish the developing embryo

What is the difference? Sex cells Vs Body cells

What type of cell division produces body cells? Mitosis = My toes

What type of cell division produces sex cells? Meiosis x

Which of the two cell divisions leads to variation? Meiosis = VARIATION Mitosis = CLONES

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 sperms 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