Chromosomes & Karyotyping

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					Chromosomes &
  Karyotyping
Human Chromosomes

 # of chromosomes in each cell varies
  from one species to the next
   Number of chromosomes does not reflect
    complexity of organism
          Gorilla – 48
          Kangaroo – 12
          Wolf – 78
          Mosquito – 6
          Ophioglossum reticulatum (species of fern) - 1260
Human Chromosomes cont’d…

       Humans have 46
    chromosomes, organized
        into 23 pairs of
        chromosomes.
   o Each pair: 1 chromosome from
         mother, 1 from father
Homologous Chromosomes
 Pairs of chromosomes that appear similar
   length
   centromere location
   banding pattern

  Homologous chromosomes
  are NOT identical!
Homologous Chromosomes cont’d…

 Chromosomes contain many genes
   Genes are sections of DNA that code for a trait
 Homologous chromosomes carry genes for the same
  trait at the same location
                  They can carry different forms
                     of the gene called alleles
    Example:
           Gene for hair colour has many possible alleles
           Allele A: blond hair, Allele B: brown hair, Allele C: red hair
      Build your own pair of
   homologous chromosomes…
 You will make a pair of
  chromosomes.
 Specific length assigned!
   Your homologous pair should
    have 3 genes.
      There are 2 alleles possible for
       each gene.
          After you have made your
           chromosomes, sketch them in
           your notes, label the genes and
           alleles.
          Come up with an example trait
           for the gene, then two possible
           forms of the trait for the alleles.
Human Chromosomes cont’d…

  23 pairs of chromosomes…
    22 pairs are called autosomes
    1 pair is the sex chromosomes
      Sex chromosomes determine sex of individual
         Female: two X chromosomes
         Male: one X, one Y chromosome
Karyotype

 Particular set of chromosomes an individual
  has
   How many karyotypes do we have in this classroom?


   To prepare karyotype:
        Stop cell during metaphase of mitosis
        Stain the cell
        Chromosomes sorted and paired, in order of longest-shortest
        Autosomes numbered 1-22
        Sex chromosomes labelled as X or Y

				
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posted:7/27/2012
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