Cellular Reproduction. MXMS 7th Grade Science

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1 Cellular Reproduction MXMS 7th Grade Science

2 What is cell division? 2 primary methods allow for cells to divide and reproduce themselves: A. Mitosis: produces identical offspring B. Meiosis: produces genetically diverse offspring

3 Mitosis

4 Mitosis 1 parent cell is able to produce 2 identical daughter cells (diploid cells) known as asexual reproduction ex: it is used in humans to repair cuts & scratches (we want identical cells for replacement!)

5 Mitosis Phases of Mitosis: A. Interphase 1. Growth phase #1 2. Synthesis phase 3. Growth phase #2 B. Prophase C. Metaphase D. Anaphase E. Telophase 1. Ends with cytokinesis

6 Mitosis Interphase is the longest phase (not officially mitosis) Includes three events: A. Growth phase #1 the cell grows to make room for duplication of its organelles B. Synthesis the cell s DNA strands are duplicated! C. Growth phase #2 the cell continues to grow

7 Mitosis Prophase: A. Nucleus itself breaks down B. Strands of DNA left behind (chromatin), condense into chromosomes

8 Chromosomes Contain the DNA of living organisms Made up of two (sister) chromatids joined in the middle (by the centromere)

9 Mitosis Metaphase: A. Chromosomes line up in the middle of the cell

10 Mitosis Anaphase: A. Chromosomes break at centromeres (middle) B. Sister chromatids move to opposite ends of the cell

11 Mitosis Telophase: A. Two new nuclei reform B. Chromosomes unwind back into chromatin strands C. Cytokinesis occurs last, physically pinching the cytoplasm in half, creating two new cells

12 Meiosis

13 Meiosis 1 parent cell is able to produce 4 genetically diverse daughter cells (haploid cells) known as sexual reproduction divided into two parts: A. Meiosis I is where crossover occurs & the parent cell splits B. Meiosis II is very similar to Mitosis, where the two remaining daughter cells are split again to produce four cells with half the chromosomes ex: it is used to produce humans (we all look different for a reason!)

14 Phases of Meiosis: A. Interphase 1. Growth phase #1 Meiosis 2. Synthesis phase 3. Growth phase #2 B. Prophase #1 C. Metaphase #1 D. Anaphase #1 E. Telophase #1 F. Prophase #2 G. Metaphase #2 H. Anaphase #2 I. Telophase #2 4. ends with Cytokinesis

15 Meiosis Interphase is the longest phase (not officially meiosis) Includes three events: A. Growth phase #1 the cell grows to make room for duplication of its organelles B. Synthesis the cell s DNA strands are duplicated! C. Growth phase #2 the cell continues to grow

16 Meiosis I Prophase # 1: A. Nucleus itself breaks down B. Strands of DNA left behind (chromatin), condense into chromosomes C. DNA is exchanged as chromosomal crossover occurs this leads to the genetic diversity in each of us

17 Meiosis I Metaphase # 1: A. Homologous chromosomal pairs line up in the middle of the cell

18 Meiosis I Anaphase # 1: A. Homologous chromosomal pairs separate and move to opposite ends of the cell

19 Meiosis I Telophase # 1: A. Two new nuclei reform B. Chromosomes unwind back into strands of chromatin C. Cytokinesis splits the parent cell into two new daughter cells

20 What do we have? Before beginning Meiosis II, let s recap: A. 1 parent cell has split into 2 daughter cells B. Each daughter cell has the same # of chromosomes as the parent cell originally C. BUT the DNA of the chromosomes are genetically different (due to crossover)

21 Meiosis II (we are now dealing with 2 cells simultaneously) (Interphase DID NOT occur again what does this mean?) Prophase # 2: A. Nuclei break down B. Strands of DNA left behind (chromatin), condense into chromosomes

22 Meiosis II Metaphase # 2: A. Chromosomes align in the middle of each cell

23 Meiosis II Anaphase # 2: A. Chromosomes break at centromeres (middle) B. Sister chromatids move to opposite ends of each cell

24 Meiosis II Telophase # 2: A. Four new nuclei reform (two cells splitting into four total) B. Chromosomes unwind back into chromatin strands C. Cytokinesis occurs last, physically pinching the cytoplasm in half, creating four new cells

25 What do we have? After Meiosis II, let s recap: A. 2 cells have split into 4 daughter cells B. Each daughter cell now has half the # of chromosomes as the parent cell originally (haploid cells) C. AND, remember the DNA of the chromosomes are genetically different (due to crossover in Prophase I) D. these 4 new, genetically diverse cells are gametes (sex cells with 23 chromosomes each), also known as sperm & egg cells E. note that the original parent cell had 46 chromosomes, so when these gametes combine later, the new cell will have 46 chromosomes also

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