1.6-mitosis and meiosis

• Interphase of mitosis and meiosis 1


  It is the longest phase. It comes between successive cell divisions. DNA replicates allowing for the double stranded chromosomes, as sister chromatids joined by a centromere, which later divide. Cellular structures are made. A significant proportion of time is spent checking genetic information
• Prophase of mitosis and meiosis 1


  The chromosomes condense into chromatids and become visible. Nuclear membrane disappears. Each consists of paired chromatids. Held together at the centromeres. Homologous chromosomes pair up. Chromosomes entwine forming chiasmata. Crossing over by breaking and interchange of DNA.
• Metaphase of mitosis and meiosis 1


  The spindles appears. Bivalents move to equator. Chromosomes attach to spindle at centromeres. Centrioles move to opposite poles.
• Anaphase of mitosis and meiosis 1


  It is a very rapid stage. The centromere separates and the spindle fibers shorten, pulling the now separated chromatids to the poles. Random assortment occurs.
• Telaphase of mitosis and meiosis 1


  This is the final stage in mitosis. The chromatids have reached the poles of the cell and now are called chromosomes again. The chromosomes uncoil and lengthen, the spindle fibers break down and the nuclear envelope reforms.
• Cytokinesis


  The division of the cytoplasm to make two new cells.
• Chromosome number


  Each chromosome in the daughter cell is an exact replica of thoses in the parental cell. So mitosis produces cells that are genetically identical to the parent giving genetic stability.
• Asexual reproduction


  Produces complete offspring that are genetically identical to the parent.
• Cytokinesis 1


  The division of the cytoplasm, occurs making two haploid cells.
• Interphase 2 of meiosis


  The cell replicates its chromosomes

  Each chromosome has two sister chromatids held together by a centromere.
• Prophase 2 of meiosis


  A spindle forms in each of the two new cells and the fibers attach to the chromosomes.
• Metaphase 2 of of meiosis


  The chromosomes are pulled to the center of the cell and line up randomly at the equator.
• Anaphase 2 of meiosis


  The centromere of each chromosome splits

  The sister chromatids separate and move to opposite poles
• Telophase 2 of meiosis


  Nuclei reform

  The spindles break down

  The cytoplasm divides
• Cytokinesis 2


  Produces four haploid daughter cells.
• Mitosis


  Number of divisions - 1

  Number of daughter cells - 2

  Chromosome number in daughter cell - same as parent cell

  Ploidy of daughter cells of diploid parent cell - diploid

  Chiasmata - Absent

  Genetic crossing over - None

  Independent assortment - None

  Genetic composition - Identical
• Meiosis


  Number of divisions - 2

  Number of daughter cells - 4

  Chromosome number in daughter cell - half as parent cell

  Ploidy of daughter cells of diploid parent cell - Haploid

  Chiasmata - Present

  Genetic crossing over - Prophase 1

  Independent assortment - Metaphase 1&2

  Genetic composition - Different
• Crossing over

  A process that occurs during meiosis, where sections of homologous chromosomes exchange genetic material, resulting in new combinations of genes on each chromosome. This helps to increase genetic diversity in offspring.
• How crossing over increases genetic diversity

  Crossing over shuffles genes and creates new combinations of alleles (different versions of a gene) on each chromosome. This allows for a greater range of genetic variation within a population, which can lead to increased adaptability and survival of the species.
• Source of variation from meiosis

  1. Crossing over at Chiasmata during PROPHASE 1.
• genetic variation-meiosis


  2. Independent assortment HOMOLOGOUS CHROMOSOMES during Metaphase 1. The daughter cells contain different combinations of maternal and paternal chromosomes.
• genetic variation- meiosis


  Independent assortment of chromatids during Metaphase 2. Daughter cells have different combinations of chromatids.
• diploid

  2 complete sets of chromosomes
• haploid


  one complete set of chromosomes- ONLY in mitosis. eg. gametes
• oncogene

  gene potentially can form cancer
• cancer


  caused by uncontrollable mitosis
• meiosis


  2 stage cell division in sexually reproducing organisms that produces 4 genetically daughter cells each with Half the number of chromosomes of the parent cell. In meiosis 1, homologous chromosomes separate, in meiosis 2 chromatids separate.
• chiasma-plural=chiasmata


  site at which chromosomes exchange DNA in genetic crossing over
• independent assortment


  either a pair of homologous chromosomes moves to either pole at anaphase 1 of meiosis, independently of the chromosomes of other homologous pairs