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UNIT 7: Cell Division

UNIT 7: Cell Division. BIG IDEA: Cell division is the process in the body to create more cells and gametes . Chromosome Structure. Inside your nucleus are 3 billion nucleotides of DNA In order to fit it is coiled and packed into a complicated but organized structure. Chromosome Structure.

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UNIT 7: Cell Division

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  1. UNIT 7: Cell Division BIG IDEA: Cell division is the process in the body to create more cells and gametes

  2. Chromosome Structure • Inside your nucleus are 3 billion nucleotides of DNA • In order to fit it is coiled and packed into a complicated but organized structure

  3. Chromosome Structure • Histones-Proteins that DNA are wrapped around

  4. Chromosome Structure • Chromatin-Less tightly coiled DNA wrapped around a histone

  5. Chromosomes • Rod shaped structures made up of DNA and histones • Two identical halves are called chromatids • Point holding together the chromatids is called a centromere

  6. Chromosomes • Structure in cells that undergo division and that contain hereditary information of the organism • In mitosis the chromosomes that undergo cellular division are called autosomes

  7. Chromosomes • Draw a chromosome and label the centromere and the chromatids

  8. How many chromosomes are present in an autosomal cell? • 23 pairs or 46 chromosomes • Refers to DIPLOID: meaning that a cell possesses 2 complete sets of chromosomes

  9. Why are there two sets of chromosomes? • 1 set is from your mother and 1 set is from your father • This leads to genetic variation because genetic information on chromosomes from your parents can be different • Example: both chromosomes can code for eye color except one can be for blue eyes and one for green eyes

  10. Black Hair Genetic Variation Blonde Hair

  11. Why is genetic variation beneficial? • Causes a diverse collection of genes • Increase in survival

  12. MITOSIS • Cell division that produces two identical diploid daughter cells • Every body cell has a life span called the cell cycle so cells must divide to replace themselves • Cells also divide in order for organisms to grow

  13. CELL CYCLE • Cycle that a cell goes through in order to make new cells • If an organism is unicellular, than a new organism is created via the cell cycle

  14. Asexual Reproduction • Reproduction with only one parent • offspring are identical to parents

  15. Sexual Reproduction • Requires 2 parents • New individual is produced by the union of the nuclei of two specialized cells (sperm & egg) • We all start off as a single cell-the cell cycle and division made you what you are today

  16. Cell Cycle Consists of Two Parts: • Mitosis: • Division of the nucleus to form two identical nuclei • REMEMBER: Hereditary material is found in the nucleus • Cytokinesis • Division of the cytoplasm of the cell after mitosis

  17. INTERPHASE

  18. Interphase • Stage when a cell is between mitotic cycles: A. G1- cell grows B. S- DNA replication C. G2- Organelle replication

  19. MITOSIS

  20. Prophase • Chromosome become visible • Centrioles move to opposite poles of the cells • Microtubules form spindles • Spindle fibers become attached to centromeres • Nuclear membrane disappears • Nucleolus disappears

  21. Prophase:

  22. Metaphase • Chromosomes attach to the microtubule spindles • Chromosomes line up on the equator of the cell

  23. Anaphase • Centromeres double • Chromosomes(sister chromatids) move to opposite poles • Division (cleavage furrow) appears

  24. Telophase • Begins when chromosomes reach the poles • Chromosome uncoil and become invisible • Spindle disappears • Nuclear membrane forms • Nucleioli reappears

  25. Telophase

  26. Cytokinesis in Animal Cells • Begins during late anaphase • Cytoplasm is pinched off by cell membrane

  27. Mitosis & Cytokinesis in Plant Cells • Main events are the same • Plants do not have centrioles or asters • Cytokinesis cannot occur by pinching off of membrane a cell plate forms between the new cells during anaphase or telophase

  28. Cytokinesis End with two identical daughter cells

  29. Cells that divide rapidly • Plants • Animals

  30. Cells that seldom or never divide • Xylem (part of a plant) • Nerve Cells • Muscle Cells

  31. Meiosis Remember-mitosis is cell division in autosomes (all cells except sex cells) Meiosis is the creation of haploid sex cells for reproduction

  32. What is the function of a haploid cell? • Used in sexual reproduction • EX: sperm for males & egg for females • During fertilization haploid sperm and haploid egg combine to form a diploid cell

  33. How does meiosis begin? Once diploid cells in reproductive organs have replicated DNA and they are no longer in interphase meiosis starts

  34. Stages of Meiosis: Same as mitosis EXCEPT there are two for each stage (i.e. Prophase I and Prophase II)

  35. Prophase I Chromosome condense from chromatin Nuclear Membrane Disappears Spindle fibers develop on which chromosomes group together Homologous chromosomoes align

  36. Prophase I continued • The pairs of chromosomes are called a tetrad and the pairing up is called synapsis • Chromatids may break off and attach to adjacent chromatids-called crossing over. • Exchange of genetic material between parental chromosomes creates genetic recombination

  37. Metaphase I Duplicated chromosomes line up in the middle of the cell.

  38. Anaphase I Chromosomes move to opposite poles

  39. Telophase I One set of each chromosome ends up in each new nucleus and the cytoplasm divides

  40. At this point we have two DIFFERENTdiploid cells Now these two cells will go through the phases again

  41. Prophase II Spindle fibers form Chromosomes move toward the middle of the spindle

  42. Metaphase II • Spindle fibers attach to centromere of chromosomes and chromosomes are in the middle of the cell.

  43. Anaphase II Chromosomes separate and move toward opposite ends of the cells

  44. Telophase II Daughter cells divide to form 4 haploid cells Chromosomes return to their interphase or “resting” form

  45. At the end of meiosis… • Result in 4 cells • Either sperm or egg cells • Each cell possesses half the number of chromosomes of the parent (or 23 chromosomes)

  46. Why is the number of chromosomes reduced by half? Cells have divided two times but DNA was only replicated once

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