SBI3U - Genetics Unit 3

• Karyotype

  The particular set of chromosomes that an individual has
• Human somatic cells have 46 chromosomes, organized into 23 pairs

  
• Chromosome pair


  1 chromosome from parent 1, 1 chromosome from parent 2
• Sex chromosomes


  X & Y
• Autosomes


  All other chromosomes besides the sex chromosomes
• Chromosomes are paired


  Based on sharing similar characteristics (length, centromere location, and banding pattern)

  
• Genetics


  The field of biology that involves the study of how genetic information is passed from one generation to the next
• Cell theory


  • All living things are composed of one or more cells
  • Cells are the smallest units of living organisms
  • New cells come only from pre-existing cells by cell division
• Functions of cell division


  • Growth of the organism
  • Repair of tissues and organs
  • Maintenance to replace dying or dead cells
• All somatic cells (body cells of plants and animals) go through cell cycles of 12-24 hours
• Traits are passed from one cell (the parent cell) to new cells (the daughter cells)
• The Cell Cycle


  1. Interphase

  2. Mitosis

  3. Cytokinesis

  
• Interphase


  Cell grows & prepares for division, divided into G1, S, G2 phases

  
• Interphase


  • Making many new molecules
  • DNA is replicated (copied)
  • DNA exists as uncondensed fibres called chromatin
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase

  
• Mitosis


  • Accurate separation of the cell's replicated DNA to enable the cell's genetic information to pass into the new cells, resulting in 2 genetically identical cells

  
• Prophase


  1. Chromatin condenses into chromosomes

  2. Nuclear membrane breaks down

  3. Nucleolus disappears

  4. Spindle fibres (made of microtubules) are formed from the centrosomes as they move apart to opposite poles of the cell

  5. Spindle apparatus moves and organizes the chromosomes

  
• Metaphase


  1. Spindle fibres guide the chromosomes to the equator (centre line) of the cell

  2. Spindle fibres from opposite poles attach to the centromere of each chromosome
• Anaphase


  1. Centromere splits apart

  2. Sister chromatids separate from each other

  3. Spindle fibres shorten, pulling the chromosomes to opposite poles of the cell
• Telophase

  1. Chromosomes unwind into strands of less-visible chromatin

  2. Spindle fibres break down

  3. Nuclear membrane forms around the new set of chromosomes

  4. A nucleolus forms within each new nucleus
• Cytokinesis


  1. Division of the cytoplasm

  2. Indentation forms in the cell membrane along the equator of the cell

  3. Deepens until the cell is pinched in two (by microfilaments)

  4. Cytoplasm divides equally between the two halves of the cell

  
• Cytokinesis in Plant Cells

  • A plant cell has a rigid cell wall covering its cell membrane (does not pinch in)
  • Instead, a cell plate forms between the two daughter nuclei
  • Cell walls form on either side of the cell plate creating 2 genetically identical plant cells

  
• Cytokinesis in Prokaryotic Cells

  • Lack of nucleus
  • Cell division is completed by a process called binary fission
  • When prokaryotic DNA is duplicated, both copies attach to the cell membrane
  • As the cell membrane grows, the attached DNA molecules are pulled apart
  • The cell completes fission, producing two new prokaryotic cells

  
• DNA nucleotide


  • Phosphate group
  • Sugar group
  • Base
• DNA bases


  • Adenine (A)
  • Guanine (G)
  • Thymine (T)
  • Cytosine (C)
• Complementary base pairs


  • Adenine on one strand pairs with thymine on the opposite strand
  • Guanine on one strand pairs with cytosine on the opposite strand
• DNA mutation


  A change in the nucleotide sequence of DNA
• Genome


  The complete DNA sequence in every cell of an organism
• Meiosis


  Sexual reproduction process that produces genetic variety

  
• Sexual Reproduction


  • Produces genetic variety
  • Genetic information is inherited from two parents
  • Each parent contributes a copy of half of its genetic information
  • Offspring are genetically different from their parents and each other
• Sexual Reproduction Depends on Meiosis
• Germ cell


  A cell that performs meiosis to produce gametes
• Somatic cell


  A non-reproductive cell
• Haploid


  A cell that contains 1 copy of every chromosome
• Diploid


  A cell that contains 2 copies of every chromosome

  
• The parents produce their gametes (sex cells) by meiosis
• When two sex cells undergo fertilization (fusion – also known as conception) a zygote is made – the first cell of a new organism
• Meiosis


  • Ensures gametes (sex cells) have the right type and number of chromosomes for when they later join to form the zygote (the fertilized cell)
  • Occurs in the reproductive organs of sexually reproducing organisms (i.e. testes for males and ovaries for females)

  
• Humans have 46 chromosomes, with sex chromosomes being haploid (half)
• Sperm


  Produced from diploid cells (in the testes) called "spermatogonium"