Mitosis + Meiosis

• DNA


  Controls the structure and actions of cells
• DNA in cell reproduction

  • Each new cell gets exactly the same DNA as the parent cell
  • Cells are genetically identical
• Cell division


  1. Mitosis

  2. For growth (new cells) and repair (replace old cells)
• Mitosis


  Division of the nucleus
• Somatic cells


  Normal everyday cells, distinct from reproductive cells
• Cell division for reproduction


  Meiosis
• Cytokinesis


  Division of cytoplasmic contents
• Mitosis


  Copies DNA of the nucleus
• Cytokinesis


  Divides cytoplasm and organelles
• Binary fission


  Division of prokaryotic cells
• Haploid


  Cells with one set of chromosomes (one gene per trait)
• Diploid


  Cells with homologous chromosomes (two genes per trait)
• Haploid cells


  • Gametes (sex cells)
• Diploid cells


  • Somatic (body) cells
• Cell cycle


  1. G1

  2. S

  3. G2

  4. M

  5. C
• G1 phase


  Period of cell growth
• S phase


  DNA replication occurs
• G2 phase


  Cell checks new chromosomes for errors and makes preparations for division
• M phase


  Division of cell DNA to create two new cells
• C phase


  Division of cytoplasmic contents by cytokinesis
• G0 phase


  Cell has exited the cell cycle and is not preparing to divide
• Cells in G0 phase can re-enter the cell cycle if they receive the correct stimuli
• Changes during cell cycle

  1. Cellular volume increases

  2. DNA content doubles
• Apoptosis is the programmed organised process of cell death
• Apoptosis is a normal part of development and maintenance of an organism
• Failures in apoptosis are a major cause of cancer in which cells survive and proliferate uncontrollably
• Mitosis Chromosomes

  • Before Interphase = 46 chromosomes, 46 chromatids
• Mitosis Chromosomes:

  After Interphase = 46 chromosomes, 96 chromatids
• Mitosis Chromosomes:

  • After Mitosis = 46 chromosomes, 46 chromatids
• Gametes

  Sex cells
• Gametes

  • Contain half the normal number of chromosomes
  • Called the haploid number
  • Symbol: n
• Homologous pairs

  Apart from sex chromosomes both chromosomes in a pair contain the same genes
• Homologous pairs

  They are homologous pairs of chromosomes
• Although they contain the same genes e.g. hair colour they may be different versions of the same gene(alleles) e.g. blue/brown hair
• One chromosome may have one allele for blue eyes and the other chromosome may have the allele for brown eyes
• Homologous chromosomes

  Pairs of chromosomes (maternal and paternal) that are similar in shape and size<|>Each gene is in the same position on homologues
• • Humans have 23 pairs of homologous chromosomes
  • 22 pairs of autosomes
  • 1 pair of sex chromosomes
• Meiosis - reduction division

  The process by which gametes (sex cells) are produced with half the number of chromosomes (haploid)<|>During meiosis diploid cells are reduced to haploid cells<|>Diploid (2n) - Haploid (n)
• Meiosis

  • Meiosis is two cell divisions
  • Called meiosis 1 and meiosis 2
  • But there is only one duplication of chromosomes
• Meiosis produces diploid (2n) cells