Do Now What is the purpose of Mitosis? If a cell that has 12 chromosomes in interphase goes through mitosis, how many chromosomes will be in each cell? How is a baby made? (on a CELLULAR level…)

Objectives To list the steps of Meiosis. To compare and contrast Meiosis and Mitosis. To explain why Meiosis is necessary.

Meiosis Purpose: to make sex cells Gamete: sex cell Male gamete= sperm Female gamete= egg (ovum)

Lets take a look at our cells Somatic cells: Non-sex Cells Our Somatic Cells contain 46 chromosomes 1 chromosome from Mom, and 1 from Dad. These are called homologous chromosomes. Each gamete (sex cell) contains only 23 chromosomes! Why are there are only 23 chromosomes in our sex cells but our somatic cells have 46?

Diploid vs. Haploid Diploid cell Haploid cell Any cell with 2 homologous chromosomes Abbreviated as 2n Ex. Somatic Cells Haploid cell Any cell with a single chromosome set Abbreviated as n Ex. Gametes

How do we become a Diploid Zygote? Haploid egg cell fuses with haploid sperm cell in a process called Fertilization. Half from mom and half from dad make up our homologous chromosomes! (23 pairs) Our cells then undergo mitosis to create us. But how did our parents create the sex cells to produce us?

Meiosis Two divisions: Each are similar to mitosis Meiosis I and Meiosis II Each are similar to mitosis Produces 4 daughter cells Phases are still IPMAT, however there are two of each of the PMAT phases.

Meiosis: 2 Divisions Meiosis I: Meiosis II: Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 and cytokinesis Meiosis II: Prophase 2 Metaphase 2 Anaphase 2 Telophase 2 and cytokinesis

Crash Course Biology! https://www.youtube.com/watch?v=qCLmR9-YY7o

Prophase I Pairing of homologous chromosomes occurs forming a tetrad. (synapsis) Nuclear envelope breaks down. Crossing over can occur- homologous chromosomes exchange genetic material.

Crossing Over Crossing over does NOT occur during mitosis. Allows recombination of genes between chromosomes How is crossing over related to genetic variation?

Metaphase I Chromosome centromeres attach to spindle fibers Homologous chromosomes line up at the equator.

Anaphase I Homologous chromosomes separate and move to opposite poles

Telophase I and Cytokinesis The spindles break down. Chromosomes uncoil and form two nuclei. The cell divides, forms two new cells.

At the end of PMAT 1 … You have two cells. They are NOT genetically identical because of the crossing over Next, those two cells go through PMAT again.

Prophase II Chromosomes condense. Spindles form in each new cell Spindle Fibers attach to chromosomes

Metaphase II Chromosomes Line up at equator of each cell

Anaphase II The sister chromatids are pulled apart at the centromere by spindle fibers Move toward the opposite poles of the cell.

Telophase II and Cytokinesis The chromosomes reach the poles, and the nuclear membrane and nuclei reform. Spindle breaks down Cytokinesis results in FOUR haploid cells Each with n number of chromosomes.

At the end of meiosis We have 4 haploid offspring cells. All Genetically DIFFERENT!!