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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!. - PowerPoint PPT Presentation
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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 = 9How 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