mitosis/meiosis

• the cell cycle:

  • interphase
  • prophase
  • metaphase
  • anaphase
  • telophase
  • cytokinesis
• mitosis:

  1. prophase - podgy
  2. metaphase - middling
  3. anaphase - away
  4. telophase - tuck in
• prophase (mitosis):

  • the chromosomes condense and become visible
  • the centriole divides and they migrate to opposite poles of the cell
  • the nucleolus shrinks and disappears
  • the nuclear envelope disintegrates
• metaphase (mitosis):

  • the centrioles' spindle is formed
  • spindle fibres attach to the centromere of the chromosomes
  • chromosomes are pulled to the equator of the cell
• anaphase (mitosis):

  • spindle fibres contract
  • the centromere divides
  • chromatids are pulled to opposite poles of the cell
  • each half of the cell recieves one chromatid from each chromosome
• telophase (mitosis):

  • chromatids begin to uncoil at the poles of the spindle
  • when they reach the poles of the spindle the chromatids are known as daughter chromosomes
  • daughter chromosomes become less distinct
  • nuclear envelope reforms
• cytokinesis (mitosis):

  • the cytoplasm divides
  • two identical daughter cells are formed
• chromatid: two chromosomes joined together
• histones: proteins that cause the chromosomes to condense and become visible during prophase
• allele: different versions of the same gene (dominant & recessive)
• locus: location of the gene on the chromosome
• crossing over: chromosomes are entangled and share genes
• interphase (mitosis): the cell grows and prepares to divide. chromosomes and some organelles are replicated and chromosomes begin to condense
• meiosis is a form of cell division that gives rise to genetic variation. the main role of meiosis is production of haploid gametes as cells produced by meiosis have half the number of chromosomes.
• meiosis produces genetically different cells, genetic variation is achieved through:

  • crossing over of chromatids - pairs line up and exchange some of their genetic material
  • independant assortment of chromosomes
• meiosis is a two phase process in which 4 haploid gametes are generated from a diploid cell.
• meiosis I:

  • prophase I
  • metaphase I
  • anaphase I
  • telophase I
• meiosis II:

  • prophase II
  • metaphase II
  • anaphase II
  • telophase II
• prophase I (meiosis I):

  • chromosomes condense and become visible
  • homologous pairs form a bivalent
  • nucleolus disappears
  • spindle forms
• metaphase I (meiosis I):

  • bivalents randomly line up on the equator of the cell
• anaphase I(meiosis I):

  • homologous chromosomes in each bivalent are pulled to opposite poles
• telophase I(meiosis I):

  • two new nuclear envelopes form around haploid nuclei
  • cell divides by cytokinesis
• prophase II (meiosis II):

  • nucleolus disappears
  • chromosomes condense and become visible
  • spindle forms
• metaphase II (meiosis II):

  • chromosomes arrange themselves on the equator
  • chromosomes attach by centromere to the spindle fibres
• anaphase II (meiosis II):

  • centromeres divide
  • chromatids pulled apart to opposite poles of the cell
• telophase II (meiosis II):

  • nuclear envelopes reform around haploid nuclei
  • cell divides by cytokinesis
• haploid gametes fuse in fertilisation to form a diploid zygote
• meiosis:

  • a reduction division
  • daughter cells have half the original number of chromosomes
  • daughter cells are haploid
  • can be used for sexual reproduction
  • source of genetic variation