Continuity of life

• Cytokinesis is the division of the cytoplasm at the end of mitosis to produce two new daughter cells
• Interphase is the longest stage of the eukaryotic cell cycle
• Mitosis is important for the growth of tissue and repair and replacement of cells
• Mitosis


  • Produces two genetically identical diploid daughter cells
• Summarise the process of mitosis

  1. Prophase = nuclear envelope breaks down, chromosomes condense, centrioles move to opposite poles of the cell

  2. Metaphase = sister chromosomes line up at the equator, centromeres attach to the spindle fibres

  3. Anaphase = sister chromatids separated and pulled apart to opposite poles

  4. Telophase = nuclear envelope reforms, spindle fibres break down, chromosomes uncoil
• Stages of mitosis


  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Interphase


  • Cells grow and synthesise new organelles, proteins and DNA in preparation for mitosis
• Comparison of mitosis in plant and animal cells

  • Animal cells: Occurs in most tissues, Before mitosis, cell becomes rounded, Involves centrioles, Involves microfilaments
  • Plant cells: Occurs in meristematic cells only, Cell does not change shape, No centrioles involved, No microfilaments involved
• Stages of mitosis
• Mitosis is a form of cell division
• Sister chromatids are a pair of identical chromatids formed by DNA replication, joined by a centromere
• Meiosis is a form of cell division that produces four genetically different daughter cells (gametes) with a haploid number of chromosomes and involves two divisions
• During meiosis I, homologous chromosomes pair to form bivalents, crossing over occurs at chiasmata, and the cell divides into two with independent segregation of homologous chromosomes, each cell containing either a maternal or paternal copy
• Unrestricted mitosis may lead to cancerous growths
• Meiosis I is the first stage of meiosis where homologous chromosomes are separated to form two haploid cells
• Cross
• The significance of meiosis in reproduction is that gametes must be haploid so that when they combine during fertilisation, the full number of chromosomes is present within the resulting zygote, and it also creates genetic variation
• Homologous chromosomes are pairs of chromosomes with genes at the same locus, one maternal and one paternal, where some alleles may be the same while others are different
• How meiosis produces genetic variation
• Homologous chromosomes

  • Pair of chromosomes with genes at the same locus
  • One maternal and one paternal
  • Some alleles may be the same while others are different
• Diagram cells after each stage of meiosis

  Draw diagrams to illustrate the stages of meiosis II
• Stages of meiosis II

  1. Prophase II

  2. Metaphase II

  3. Anaphase II

  4. Telophase II

  5. Cytokinesis
• sexual reproduction


  reproduction that results from combining genetic material from two individuals.

  
• meiosis


  type of cell division that results in 4 daughter cells that each have half the number of chromosomes as the parent cell.

  
• Diploid


  A cell containing two full sets of chromosomes 2n=46.

  
• Haploid


  A cell containing a single/ half set of chromosomes n=23

  
• Gametes


  A haploid male or female germ cell (e.g. sperm and egg)

  
• gene


  a section of the DNA (chromosome) that codes for a specific trait (e.g. eye color or hair color)

  
• crossing over


  when homologous chromosomes exchange genes during Prophase 1 creating new mixture of parent traits in their offspring

  
• Meiosis I


  PMAT I: The first cell division of meiosis when the homologous pairs are split up into two separate cells.

  
• Meiosis II


  PMAT II: The second cell division of meiosis. This is when the sister chromatids are split up into two separate cells.

  
• Mitosis


  Produces cells almost genetically identical
• Asexual reproduction


  Has the advantage of producing offspring in greater numbers, with no partner required
• 23 pairs of chromosomes


  How many pairs of chromosomes present in humans
• Chromosome


  Coiled up DNA

  
• Chromatin


  Uncoiled DNA. Present in interphase

  
• Homologous Chromosomes


  Carry the same genes at the same locus (location).

  Ex. Chromosome 1 and Chromosome 1

  
• Function and location of Mitosis

  Cell division for growth, repair or maintenance. Occurs in body cells.

  PMAT
• Function and location of Meiosis

  Cell division for gamete production (sperm and eggs).

  PMATPMAT
• Phases of the Cell Cycle

  1. Interphase (G1, S, G2)

  2. Mitosis (PMAT)

  3. Cytokinesis (cell division)