Chromosome

							Chromosomes
      Chromosome Structure
                 (Eukaryotes)

   Rod-shaped structures made of DNA
    and proteins
   Located in the nucleus
   Histones-proteins that help maintain the
    shape of the chromosome and aid in the
    tight packing of DNA
   Nonhistone-proteins that control the
    activity of specific regions of the DNA
   Chromatid- page 244- two identical halves
    (forms as the DNA makes a copy of itself
    before cell division)
   Centromere- constricted area of the two
    chromatids (center of the ‘X’ shape)
   The centromere holds the two chromatids
    together until they separate during cell division
   Chromatin- less tightly coiled DNA-protein
    complex
       Chromosome Numbers
   Each species has a           # of
    characteristic     Organism Chromosome
    number of
    chromosomes in     Humans    46
    each cell          Fruit Fly 8
                       Earthworm 36
                       Carrot    18
                       Horse     64

                    Dog       78
         Sex Chromosomes and
              Autosomes
   Human and animal chromosomes are
    categorized as either sex chromosomes or
    autosomes
   Sex Chromosomes-chromosomes that
    determine the sex of the organisms and other
    characteristics (human-either XX or XY)
   XX-female
   XY-male
   Autosomes-all other chromosomes
   Each cell has 2 copies of each autosome
    • One from each parent
   Homologous Chromosomes-pair of
    autosome
    • Homo---same
    • Same size, shape and carry genes for the
        same trait (ex-eye color, hair color, height)
    •   Humans have 22 homologous pair of
        chromosomes (= 44 chromosomes)
   Sex cells make up the other pair of
    chromosomes making the total for
    humans 46 (or 23 pair)
   Karyotype-page 341-photomicrograph of
    chromosomes
     Diploid and Haploid Cells

   Diploid Cells— cells containing two sets
    of Chromosomes (homologous pair)
    • Also have two sex chromosomes in each cell
      (XX, XY)
   Haploid Cells– cells containing one set
    of chromosomes (reproductive cells)
    • Sperm cells
    • Egg cells