Mitosis, meiosis, and mendel

• DNA


  The molecule that transfers hereditary information from one cell to the next
• Gene


  A specific portion of the DNA code that has genetic information

  
• Chromosome


  Structures formed by tightly wound DNA during cell division

  
• For most of the life of the cell, chromosomes are too elongated to be seen under a microscope
• Chromosome duplication before mitosis

  1. Chromosomes are duplicated

  2. Condensed into short structures

  3. Held together at centromeres

  4. Called sister chromatids
• A karyotype is a picture showing the arrangement of a full set of human chromosomes

  
• Humans have 46 (or 23 pairs) of chromosomes
• Somatic cells


  Diploid cells (2N) with two chromosomes of each type
• Gamete cells


  Haploid cells (1N) with only one of each type of chromosome
• 2N


  Symbol for diploid
• 1N


  Symbol for haploid
• The cell cycle


  1. Interphase

  2. M stage (mitosis and cytokinesis)
• Mitosis


  1. Sister chromatids separate

  2. Become nuclei of daughter cells
• The cell cycle ends when cytokinesis is complete
• Mitosis


  The process by which somatic (body) cells reproduce themselves
• All somatic cells are diploid (2N) and both daughter cells produced are also diploid
• Mitosis leads to the production of two daughter cells
• Each daughter cell has the same number of chromosomes as the parent cell
• Steps of Mitosis


  • Interphase
  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase
  • Cytokinesis
• Meiosis


  The process by which gamete (sperm or egg) cells reproduce themselves
• During meiosis, a single diploid cell divides and produces four haploid reproductive cells
• Meiosis


  1. One chromosome duplication

  2. Two cellular divisions (Meiosis I and Meiosis II)
• Upon fertilization, a 1N sperm meets a 1N egg and a zygote (2N) is formed
• Steps of Meiosis I and Meiosis II

  • Late Prophase I
  • Metaphase I
  • Anaphase I
  • Telophase I
  • Prophase II
  • Metaphase II
  • Anaphase II
  • Telophase II
  • Cytokinesis
• Genetic recombination


  Occurs during meiosis through crossing-over and independent assortment
• Sources of genetic recombination during meiosis

  • Crossing-over
  • Independent assortment
  • Fertilization
• Before mitosis and meiosis, DNA replication occurs only once during interphase prior to cell division
• Mitosis requires one division while meiosis requires two divisions
• Two diploid daughter cells result from mitosis while four haploid daughter cells result from meiosis
• Daughter cells from mitosis are genetically identical to parental cells
• Daughter cells from meiosis are not genetically identical to parental cells
• Mitosis occurs in all somatic cells for growth and repair
• Meiosis occurs only in the reproductive organs for the production of gametes
• Comparison of Meiosis I to Mitosis

  • Prophase I - pairing of homologous chromosomes
  • Metaphase I - homologous pairs line up at metaphase plate
  • Anaphase I - homologous chromosomes separate
  • Telophase I - daughter cells are haploid
• Comparison of Meiosis II to Mitosis

  • Meiosis II nuclei contain haploid number of chromosomes
  • Four haploid daughter cells at end of meiosis II
  • Two diploid daughter cells at end of mitosis
• The human life cycle requires both mitosis and meiosis
• In males, meiosis occurs as spermatogenesis and produces sperm
• In females, meiosis occurs as oogenesis and produces egg cells
• Major difference between mitosis and meiosis

  Mitosis retains the same chromosome number (2N to 2N) while meiosis halves the chromosome number (2N to 1N)
• Ways meiosis and fertilization ensure genetic diversity

  • Independent assortment of chromosomes during metaphase I
  • Crossing-over during prophase I
  • Recombination of chromosomes from different individuals upon fertilization