Meiosis & Fertilization State Standard LS1I

Things to Remember 1. Asexual Reproduction All living things REPRODUCE two types of reproducing: 1. Asexual Reproduction Produces cells that are IDENTICAL copies of parent cell 2. Sexual Reproduction Combines genetic material of 2 parents so offspring are genetically DIFFERENT from parents

Sexually Reproducing Males SPERMATOGENESIS = MAKING MATURE SPERM Process occurs in the TESTES Begins with Primary SPERMATOCYTES Process of meiosis yields 4 SPERM (gametes) The process occurs constantly throughout life

Sexually Reproducing Females OOGENESIS = MAKING a Mature Egg Process occurs in the Ovaries Begins with Primary OOCYTES Process of meiosis yields 1 Egg (gametes), and 3 polar bodies Cytoplasm divides unevenly Polar bodies degenerate Females are born with a finite number of Eggs.

Interphase I Cells undergo a round of DNA replication, forming duplicate chromosomes

Prophase I Each chromosome pairs with its corresponding homologous chromosome to form a tetrad.

Metaphase I Spindle fibers attach to the chromosomes

Anaphase I The fibers pull the homologous chromosomes toward opposite ends of the cell.

Telophase I and Cytokinesis Nuclear membranes form. The cell separates into two cells.

Analysis Questions Describe in your own words the events of this first meiotic division. What other chromosomal patterns might have resulted in the daughter cells? (you may wish to move your model pieces around to help illustrate the possibilities. How many chromosomes does each daughter cell now have? What helped you determine that number?

Prophase II DNA condenses into chromosomes and spindle fibers are formed.

Metaphase II The chromosomes line up in a similar way to the metaphase stage of mitosis.

Anaphase II The sister chromatids separate and move toward opposite ends of the cell.

Telophase II Cells begin to divide, forming daughter cells.

Analysis Questions Describe in your own words what has taken place in Meiosis II. Indicate which chromosome came from which parent in each of the resulting cells. What is the difference between the starting cell (primary spermatocyte or oocyte) and the cells at the end of Meiosis I? Between the cells at the end of Meiosis I and the cells at the end of Meiosis II? Describe why you think meiosis is a significant process in terms of: The passing on of information from generation to generation Variation of traits among siblings

Meiosis Meiosis is the way to make cells with ½ the number of chromosomes for sexual reproduction Meiosis Crash Course