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Cell Reproduction

This comprehensive guide explores the intricacies of cell reproduction, focusing on mitosis and meiosis. It covers the structure and types of chromosomes, detailing the role of chromatids and centromeres. The distinction between diploid and haploid cells is clarified, along with the process of karyotyping. Mitosis is described step-by-step, highlighting its four phases: prophase, metaphase, anaphase, and telophase. Meiosis, on the other hand, is presented as a two-part division that generates genetic diversity through crossing over and independent assortment.

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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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