Mitosis and Meiosis

The Role of Mitosis Two Stages -Divide nucleus & DNA -Divide cell (cytokinesis) Purpose: to produce 2 identical cells for… -Growth -Repair of tissue -Replace dead cells -Asexual Reproduction

Terms to know! DIPLOID (2n): Full complement of chromosomes. In humans 2n = 46 HAPLOID (n): Number of unique chromosomes In humans n = 23

Diploid or Haploid? In a cabbage cell the Diploid number is 2n = 18 What is the Haploid number? n = 9 How many homologous pairs? 9

The Cell Cycle Most of the cell’s time is spent in Interphase!

Stages of Mitosis - Interphase This is the parent cell Rapid growth Cell doing its job DNA replication (chromatin) Prepares for division

Stages of Mitosis - Prophase DNA condenses into chromatids (thicker) Nuclear membrane disappears Spindle fibers form from centrioles and attach to centromeres.

Stages of Mitosis - Metaphase Chromatids line up down the middle. Pulled into place by spindle fibres.

Stages of Mitosis - Anaphase Chromatids are pulled apart (by spindle fibers)

Stages of Mitosis - Telophase Nuclear membrane reforms Cytokinesis occurs (cell divides) 2 identical daughter cells (DIPLOID – 2n)

Mitosis in Plant Cells No centrioles A cell plate forms, then cell wall.

Meiosis and Variation Variation is key for species survival, allows organisms to adapt! During Meiosis, two events occur which increase variation…

Independent (Random) Assortment When tetrads line up at Metaphase I, the paternal and maternal chromosomes line up randomly on the left and right. 223 = 8 388 608 different combinations!

Crossing Over While the dyads are in the tetrad, pieces of homologous chromatids can change places, creating different chromosomes. This is desirable and occurs frequently If one piece gets misplaced, a mutation occurs (genes are missing)

Stages of Meiosis Use your textbook (Pg. 154-155) and the handout to document the steps in Meiosis