Linkage_ Recombination and Eukaryotic Mapping

							Linkage, Recombination and
    Eukaryotic Mapping




           Part 2
                  Outline
• Gene mapping in Humans
  – Pedigrees and linkage


• Physical Chromosome mapping
          Nail-Patella Syndrome

– Autosomal dominant: abnormal fingernails and
  absent (underdeveloped kneecaps)




– ABO blood type alleles linkage
     (2 out of 13 offspring)
2/13= 0.154 recombination frequency
   Physical Chromosome Mapping
• Provides us alternative methods for gene mapping that do not rely on rates
                  of crossing over to determine gene location
    Methods that are considered “physical
        mapping of the chromosome”

• Deletion mapping

• Somatic Cell hybridization

• In Situ Hybridization

• DNA Sequencing
                        DELETION MAPPING
(this has been used to map Muscular Dystrophy gene to X chromosome




    50% have mutation                 all have normal phenotype
                 Deletion Mapping
• Can also be done with homozygous recessive
                  Crossed with
• Homozygous wt+ but with deletion(s)

                                                           Offspring will be:

                          Deletion area a            a
                                        b            b
                         B+                                     aB+
            B+


                                                                 a
                                                                 b

      We now know this deletion includes the locus that
      is within the region deleted for A+ but not for B+
You can perform this
a panel of deletions.                                 Mutations
                                                      del      a              b    c   d       e   f
                                                      1       m               +    m   +       +   m
                                                      2       m               +    +   +       +   +
                                                      3       +               m    m   m       m   +
                                                      4       +               +    m   m       m   +
                                                      5       +               +    +   m       m   +
                                                      6       +               m    +   m       +   +


                                                    a             c                        d
                                      chromosome
                                                                                                       etc.


                         deletion 1
                                  deletion 2
                                                deletion 3
                                               deletion 4
                                                             deletion 5
                                                                      deletion 6




                        f?         a f? c                          e           d                   b
              SOMATIC CELL HYBRIDIZATION



+ Human somatic cell
  You set up a panel of these hybrid cells that include a random selection of
                            human chromosomes




Look for which cell lines produce the product AND which chromosomes are
                                  present.


   Bingo! You can determine which gene is associated with which chromosome!
     In Situ Hybridization
detects genes on chromsomes
                DNA SEQUENCING




More to come with our
molecular discussions
     Practice Physical Mapping
• Questions 4, 5, 26 and 27 at the back of chapter 7 to try
  out your skills at deletion analysis and somatic-cell
  hybridization.



• I will post the answer for question 26 (others are in the
  book).

• Does not have to be handed in—just to practice to see if
  it all makes sense.
The End