Meiosis & Sexual Reproduction Ag Biology

A form cell division that halves the number of chromosomes when forming reproductive cells (gametes) What is Meiosis?

Involves 2 divisions of the nucleus: Meiosis I Meiosis II 46 Chromosomes 92 Chromosomes 46 Chromosomes Meiosis I Meiosis II 23 Chromosomes

Before meiosis begins, the DNA in the original cell is copied. Step 1: Prophase I Chromosomes condense Nuclear envelope breaks down Cross-over occurs Steps in Meiosis

Crossover occurs when portions of a chromatid are broken and exchanged with the corresponding portion of the second chromatid. What is Cross-over?

Step 2: Metaphase I Step 3: Anaphase I Pairs of homologous chromosomes move to the equator of the cell Step 3: Anaphase I Pairs of homologous chromosomes move to the opposite poles of the cell

Step 4: Telophase I & Cytokinesis Chromosomes gather at the poles of the cell Cytoplasm divides Step 5: Prophase II New spindle forms around the chromosomes.

Step 6: Metaphase II Step 7: Anaphase II Chromosomes line up at the equator Step 7: Anaphase II Chromosomes divide and move to opposite poles of the cell.

Step 8: Telophase II & Cytokinesis Nuclear envelope forms around each set of chromosomes Cytoplasm divides

Meiosis Drawing Fold a sheet of paper into 8 sections Using colored pencils, draw a cell as it goes through each of the 8 stages of meiosis Label each stage Briefly explain what occurs in each stage Make sure to put your name, date, period on it Turn in by the end of the period Meiosis Drawing

Gametogenesis Formation of gametes (sperm & eggs) In females oogenesis In males spermatogenesis Gametogenesis

Oogenesis Process by which the eggs are produced in females Occurs in the ovaries In cytokinesis following meiosis I, the cytoplasm divided unequally One cell gets nearly all the cytoplasm which will become the egg cell Cell must contain nutrients to nourish the young organism if the egg is fertilized Other cells are small and are called polar body. Polar bodies die Oogenesis

Oogenesis

Spermatogenesis Process by which sperm are produced in males Occurs in the testes 4 haploid cells are produced These cells change in form and develop a tail to become sperm Spermatogenesis