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Cell Reproduction

Cell Reproduction. Mitosis and Meiosis. Cell Reproduction. Chromosome Structure Individual chromosomes consist of 2 identical halves called CHROMATIDS The center of the chromosome is the CENTROMERE. It holds the 2 chromatids together. Chromosome. There are 2 types of chromosomes.

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Cell Reproduction

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  1. Cell Reproduction Mitosis and Meiosis

  2. Cell Reproduction • Chromosome Structure • Individual chromosomes consist of 2 identical halves called CHROMATIDS • The center of the chromosome is the CENTROMERE. It holds the 2 chromatids together.

  3. Chromosome

  4. There are 2 types of chromosomes • SEX CHROMOSOMES-determine the sex of an organism • In humans, sex chromosomes are either X or Y • FEMALES=XX • MALES=XY

  5. Types of chromosomes, cont. • AUTOSOMES-all other chromosomes • Humans have 46 chromosomes total 44 autosomes, 2 sex chromosomes • Organisms get 1 copy of each autosome from a parent-making 2 copies called HOMOLOGOUS CHROMOSOMES. They are the same size, shape, and carry the same info.

  6. VERY IMPORTANT VOCAB!! • Cells that have 2 sets of chromosomes are DIPLOID (2n). • HAPLOID (n) cells have only 1 set of chromosomes. • Sperm and egg cells are haploid cells.

  7. A KARYOTOPE is used to examine an individual’s chromosomes.

  8. Ticket to Leave • What are the 2 parts of the chromosome? • What are the two types of chromosomes in your body? • Cells that have one set of chromosomes are ______________. Cells that have two sets are ______________.

  9. Divide asexually by BINARY FISSION Produce identical offspring 3 stages DNA is copied Cell begins to divide 2 identical haploid cells are formed Cell Division in Prokaryotes

  10. Cell Division in Eukaryotes • MITOSIS • Division of all other cells • Produces 2 new identical cells, identical to the original cell • MEIOSIS • Division of the sex cells – sperm & egg • Produces 4 new similar cells, similar to the original cell

  11. Cell Division in Eukaryotes • The CELL CYCLE is the repeating set of events that make up the life of a cell. CELL DIVISION is one phase and INTERPHASE is the time between divisions.

  12. Interphase • Made of 3 phases • G1 PHASE-offspring cells grow to mature size • S PHASE-DNA is copied (REPLICATION) • G2 PHASE-cell prepares for division *Cells can exit the cell cycle and enter the G0 PHASE where DNA isn’t copied and cells don’t divide. Nervous system cells stop dividing at maturity.*

  13. Mitosis • During mitosis, the M PHASE, the nucleus of the cell divides. • 4 phases of mitosis (Interphase is before and after mitosis/cytokinesis.) • PROPHASE • METAPHASE • ANAPHASE • TELOPHASE

  14. PROPHASE • DNA coils into chromosomes • Nucleolus and nuclear membrane disappear • Dark spots appear (CENTROSOMES), which contain the CENTRIOLES (plants DO NOT have centrioles) • SPINDLE FIBERS radiate from the centrosomes

  15. METAPHASE • Chromosomes move to the MIDDLE of the cell

  16. ANAPHASE • Chromatids of each chromosome separate at centromere & move toward opposite sides of the dividing cell

  17. TELOPHASE • Spindle fibers disappear • Chromosomes uncoil • Nuclear membrane forms around each set of chromosomes • Nucleolus reforms • Telophase is almost the opposite of prophase.

  18. CYTOKINESIS • CYTOKINESIS occurs when the cytoplasm starts to divide. It starts when telophase is complete. • In animal cells, the cell membrane pinches in (CLEAVAGE FURROW) & separates the dividing cell into 2 new cells. • In plant cells, the membrane bound cell wall forms (CELL PLATE) & separates the cell into 2 new cells.

  19. Cytokinesis in animal cells

  20. Cytokinesis in plant cells

  21. Ticket to Leave • How does cell reproduction occur in prokaryotes? • What is the cell cycle? • List and briefly describe the four steps of mitosis.

  22. Meiosis • Cell division in SEX cells • Produces haploid (n) reproductive cells called GAMETES • Human gametes are SPERM & EGG • Each contain 23 chromosomes • Fusion of sperm (n) & egg (n) forms a ZYGOTE (2n) that contains 46 chromosomes **Cells begin meiosis just like mitosis—it’s just that cells divide TWICE in meiosis**

  23. Meiosis I

  24. Meiosis II

  25. DNA REPLICATION • During replication, the DNA of a 2n (diploid) cell is copied. • This only occurs before MEIOSIS I.

  26. Meiosis I • PROPHASE I • DNA coils, spindle fibers appear • HOMOLOGOUS CHROMOSOMES pair up-called SYNAPSIS (doesn’t happen during mitosis) • Portions of chromatids break off and attach to nearby chromatid on the homologous pair-called CROSSING OVER • Allows for genetic info exchange between mother/father chromosomes giving a new mixture of genetic info-called GENETIC RECOMBINATION

  27. CROSSING OVER

  28. METAPHASE I • TETRADS (each pair of homologous chromosomes) line up in middle of cell • Spindle fibers attach to the homologous chromosomes of the pair

  29. ANAPHASE I • Each homologous chromosome moves to the opposite side of the dividing cell • Random separation of the homologous chromosomes is called INDEPENDENT ASSORTMENT and it results in genetic variations

  30. TELOPHASE I • Chromosomes reach the opposite ends of cell • Each of the new developing cells will contain a haploid number of chromosomes. • CYTOKINESIS I occurs

  31. MEIOSIS II • The newly formed cells DO NOT copy their DNA. • PROPHASE II • Spindle fibers form and move chromosomes toward the middle of the cell

  32. METAPHASE II • Chromosomes move to the midline of the cells-facing opposite side of the cells

  33. ANAPHASE II • Chromatids separate and move to opposite sides of cell

  34. TELOPHASE II • Nuclear membrane forms around chromosomes in each of the 4 new cells • CYTOKINESIS II occurs resulting in 4 new cells, each containing HALF the number of chromosomes as the original cell

  35. Ticket to Leave • What is crossing over? • Meiosis is used to form __________. • List the steps of meiosis I & II. • The formation of sperm is called ___________. • The formation of eggs is called __________.

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