1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chromosomes rod-shaped structures made of DNA and protein Consist of numerous genes Humans cells have 46 each DNA wraps around proteins called histones to help maintain the compact structure Loose combination of DNA and proteins is called chromatin

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chromosome Structure Looks like an “X” –Right & Left halves are 2 identical DNA double helixes –1 half of the “X” is a chromatid –2 identical chromatids are called sister chromatids –Sisters are held together by the centromere –The tips of the “X” are called telomeres

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chromosome Structure

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Parts of a Chromosome

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chromosome Numbers of Various Organisms

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chromosomes –Sex chromosomes determine the gender of an organism –Autosomes All of the other chromosomes in an organism

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chromosome Numbers Diploid Cells Cells having two sets of chromosomes (2n) Haploid Cells –Cells having only one set of chromosomes (1n)

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mitosis divided into 4 stages 1.Prophase 2.Metaphase 3.Anaphase 4.Telophase results in two offspring cells that are genetically identical to the original cell Prokaryotes use it to reproduce Eukaryotes use it for growth, repairs, & development

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mitosis

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Stages of Mitosis 1.Prophase Chromatin condenses into tightly coiled chromosomes Nuclear envelope breaks down Nucleolus disappears Centrioles migrate to opposite poles Spindle fibers grow & move to the center of the cell

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Stages of Mitosis 2.Metaphase Spindle fibers attach to centromere Chromosomes align on cell’s equator (middle of cell)

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Stages of Mitosis 3.Anaphase Sister Chromatids separate Spindle fibers shorten Sisters are pulled to opposite poles of the cell

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Stages of Mitosis 4.Telophase Identical chromosomes are at each pole of the cell 2 Nuclear envelopes reform Chromosomes uncoil Spindle fibers fall apart

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Cytokinesis Division of the cytoplasm In animal cells, a cleavage furrow pinches in and separates the dividing cell into two cells In plant cells, a cell plate made by the Golgi Apparatus separates the dividing cell into two cells