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Chapter 6 Chromosomes and Cell Reproduction

Chapter 6 Chromosomes and Cell Reproduction. Section 6-1. Cell division (cell reproduction) Occurs in humans and LT at diff times in their life Formation of gametes (egg/sperm) involves special types of cell ÷ (this will be covered in chapter 7) When cells ÷, DNA is 1st copied and then ÷.

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Chapter 6 Chromosomes and Cell Reproduction

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  1. Chapter 6Chromosomes and Cell Reproduction

  2. Section 6-1 • Cell division (cell reproduction) • Occurs in humans and LT at diff times in their life • Formation of gametes (egg/sperm) involves special types of cell ÷ (this will be covered in chapter 7) • When cells ÷, DNA is 1st copied and then ÷

  3. Section 6-1 • Prokaryotic (Bacteria) Cell Reproduction: • Binary fission: • Form of asexual reproduction in bacteria cells that produces identical offspring • Binary fission occurs in 2 stages: 1st, DNA is copied, then cell ÷, eventually the ÷ prokaryote is pinched into 2 independent cells

  4. Section 6-1 • Eukaryotic Cell Reproduction: • Gene: piece of DNA that codes for a protein or RNA • As eukaryotic cell prepares to ÷, DNA and proteins associated w/ DNA coil into chromosomes • Chromatids: 2 exact copies of DNA that make up each chromo • Centromere: where 2 chromatids of chromo are attached

  5. Section 6-1 • Homologous chromosomes: chromo similar in size, shape, genetic content • Each homologue in a pair of homologous chromosomes comes from 1 of the 2 parents • 46 chromosomes in human somatic (body) cells are actually two sets of 23 chromosomes (23 from mom, 23 from dad) • Diploid: cell w/ 46 chromo (23 from mom, 23 from dad) • Haploid: cell w/ only 23 chromo, such as gametes • Zygote: fusion of 2 haploid gametes (fertilization) to form 1 diploid fertilized egg cell (mom’s 23 w/ dad’s 23 = 46)

  6. Section 6-1 • Autosomes: chromo not directly involved in determining sex (gender) of an individual; pairs #1-22 • Sex chromosomes: 1 pair of chromo in humans, contain genes that determine sex of individual; pair #23 referred to X and Y; XX = female, XY = male

  7. Section 6-1 • Change in Chromo #: • Humans missing 1 of 46 chromosomes usually don’t survive • Trisomy: more than 2 copies of a chromosome, will not develop properly; 3 copies of #21= Down’s Syndrome • Karyotype:photo of chromo in a dividing cell showing chromo arranged by size

  8. Section 6-1 • Change in Chromo Structure: • ∆ in organism’s chromo structure are mutations • Breakage of chromo can lead to 4 types of mutations: • 1. deletion mutation: piece missing • 2. duplication mutation: piece added • 3. inversion mutation: piece turned upside down • 4. translocation mutation: piece from chromo is put on a different chromo

  9. Section 6-2 • Cell Cycle: • Repeating sequence of cellular growth/÷ during life of organism • Interphase: • 1st 3 phases of cell cycle, 90% of cell’s time is in this phase

  10. Section 6-2 5 Phases of Cell Cycle: 1. 1st growth (G1) phase: cell grows rapidly and carries out routine functions 2. Synthesis (S) phase: DNA is copied 3. 2nd growth (G2) phase: preparations made for nucleus to ÷ 4. Mitosis: nucleus of cell ÷ into 2 nuclei 5. Cytokinesis: cytoplasm ÷

  11. Section 6-2 • Control of Cell Cycle: • Checkpoints at which feedback signals from cell can trigger or delay next phase of cell cycle • 1. Cell growth (G1) checkpoint makes decision of whether cell will ÷ • 2. DNA synthesis (G2) checkpoint DNA replication is checked by DNA repair enzymes • 3. Mitosis checkpoint triggers exit from mitosis

  12. Section 6-2 • When Control Is Lost: Cancer! • If a gene that controls cell growth/÷ is mutated, then regulation of cell growth/÷ can be disrupted = cancer and uncontrolled cell growth results! Bladder cancer

  13. Section 6-3 • Mitosis - Division of the Nucleus in 4 phases: • 1. Prophase: Nuclear envelope dissolves; spindle forms • 2. Metaphase: Chromo move to center and line up along the equator • 3. Anaphase: Centromeres ÷; chromo move to opposite ends of cell • 4. Telophase: Nuclear envelope forms around chromo at each pole; Mitosis is complete

  14. Section 6-3 • Cytokinesis – Division of the Cytoplasm: • As mitosis ends, cytokinesis begins • Cytoplasm of cell ÷ in 1/2, cell membrane grows to enclose each new cell, forming 2 separate genetically identical cells from 1 cell

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