Meiosis Why Do cells Go through Meiosis Cells

Meiosis

Why Do cells Go through Meiosis? �Cells go through Meiosis in order to make Sex Cells �Sex cells are also called Gametes �Four Daughter Cells are created �Haploid (1 N)

Interphase �Cell Grows �Duplicates DNA �Cell Prepares to divide

After Interphase �In order to make sex cells or cells with half the number of chromosomes meiosis has TWO phases �Meiosis I and Meiosis II

Prophase I �Chromosomes Condense (visible) �Homologous chromosomes form a tetrad �Crossing Over Occurs

Crossing Over �Homologous Chromosomes- Similar Chromosomes, Same genes in the same location �When the chromosomes touch they switch genes �Causes genetic variation

Metaphase I �Homologous chromosomes move together to the middle of the cell �Spindle attaches to the centromere

Anaphase I �Homologous chromosomes separate �Sister chromatids stay attached �Move towards opposite poles

Telophase I �Division of cytoplasm �Creates Two daughter cells �Begin Meiosis II �There is no interphase II �Why?

Prophase II �Spindles re-appear �Nuclear membrane stays separated

Metaphase II �Chromosomes line up in the middle �Spindle attaches �How are metaphase I and II different?

Anaphase II �Sister Chromatids Separate from each other �How are Anaphase I and II different from each other?

Telophase II �Nucleus reforms �Division into four daughter cells �Haploid (1 N) �Gametes (egg and sperm)

Mitosis & the Cell Cycle

Cell Growth & Development Are cells of organisms the same size? Do your cells get bigger as you grow, or do you just produce more cells? n When talking about Cell Size…… Smaller is Better! n The larger a cell becomes, the more demands the cell places on its DNA, and the harder it is to supply with nutrients. n

Cell Division Before a cell becomes to large, a growing cell will divide. n Cell division is the process by which a Single cell divides into 2 Daughter cells. n Cell Division = the series of events that cells go through as they grow and divide. n

Chromosomes n n n Chromosomes= are composed of DNAWhich carries the cell’s coded genetic information. Humans have 46 chromosomes(23 pairs). The chromosomes consist of two identical sister chromatids.

Two Major Types of Cell Division n Mitosis- Somatic cells (Body Cells) n n Diploid 2 N Meiosis- Sex cells/ Gametes n Haploid 1 N

Mitosis is the process by which the genetic information is replicated and distributed to daughter cells. n 2 diploid(2 N) daughter cells are produced from 1 diploid (2 N) parent cell. n The Daughter cells are genetically identical to the parent cells. n There are 4 major stages to mitosis, Not including interphase. n

Interphase n Interphase= The cell spends most of its life here; not part of the actual reproduction. NOT PART OF MITOSIS. Cell grows and replicates its DNA and centriole n Nuclear membrane is visible n Nucleus, Nucleoli, and chromatin can be seen. n

Interphase

Prophase n Prophase: first phase of Mitosis n n Nuclear membrane breaks down Chromosomes become visible n Centrioles separate n Spindle forms

Metaphase n Metaphase: Second part of Mitosis n n Chromosomes attach to spindle Chromosomes line up across the MIDDLE of the cell

Anaphase n Anaphase: Third step in Mitosis n The sister chromatids separate and move apart towards opposite poles

Telophase n Telophase: Fourth stage of Mitosis n n n Chromosomes gather at opposite ends of the cell The nuclear membrane begins to form and enclose the chromosomes Cell membrane begins to move inwards

Cytokinesis n n n Cytokinesis: Final stage in cellular division Not Mitosis Works with telophase n n The cytoplasm divides completely in half. 2 daughter cells with identical genetic information are produced.