Lecture: Linkage and Mapping

1
Lecture Linkage and Mapping
(continue)
Pedigree analysis
2
Outlines

• mapping exercise II
• Pedigree analysis
• terminology
• examples
• things to be considered

3

• What to do with genetic data for mapping
• 1) Traits are segregating?
• dominant/recessive ----gt one locus
• 2) Traits are X-linked?
• phenotype ratios differ between different
  sexes
• 3) Traits are all linked?
• case I not linked (11111111)
• ------gt may
  require ?2 test
• case II only two out of three are linked
• (10010010010050505050
  )
• -------gt find out which pair of loci
  are linked
• case III all three are linked
• (100100 2020101011)
• -----gt two-point or three-point
  mapping

4
Mapping Exercise I
phenotype in symbols
observed No. hs fm,bd,hs
2000 bd hs
fm,bd,hs 150 fm
hs fm,bd,hs 50
bd hs
fm,bd,hs 300
hs fm,bd,hs 300
bd hs fm,bd,hs
50 fm hs
fm,bd,hs 150 bd
hs fm,bd,hs
2000 Total
5000

5
Mapping Exercise I
(three-point mapping need to be sure about
linkage of all loci!)
Symbols Obs. No. fm,bd,hs
2000 fm,bd,hs 150 fm,bd,hs
50 fm,bd,hs
300 fm,bd,hs 300 fm,bd,hs
50 fm,bd,hs 150 fm,bd,hs
2000 Total 5000

Symbols Obs. No. fm,bd,hs
2000 fm, bd, hs 2000 fm,bd,hs
150 fm, bd, hs 150 fm,bd ,hs
300 fm, bd, hs 300 fm,bd, hs
50 fm, bd, hs
50 Total 5000

1.Rec. freq btw bd - hs
2. Rec. freq btw fm - bd
3. Rec. freq btw fm - hs
Final map ( ) ( ) fm - bd - hs
( )
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Double crossing-over
hs
fm
bd
Meiosis of F1
x
x
fm
hs
bd
Gametes
hs
fm
fm
bd
hs
bd
Parental
Recombinant (double Crossing-over)
hs
fm
fm
bd
hs
bd
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Mapping exercise II
P a drosophila female with yellow body
y, forked bristles f, curly wing c,
X a male with extra bristles

curly wing -------gt
half of both female and male F1
yellow body ------gt all the
male of F1
forked bristles ----gt none

extra bristles
----gt none
F1 normal F1
female X multiple homozygous male
F2 offspring 29 yellow body
25 yellow body, forked extra bristles
28 forked extra bristles 26
normal 75 extra bristles 74 yellow
body, extra bristles 72 forked bristles
71 yellow body, forked bristles
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Mapping exercise II

• Things to be considered to explain genetic
  linkage and mapping
• summarize each trait based on the inheritance
  patterns observed in P through F2
• curly
• yellow
• extra bristles
• forked bristles
• how many traits are involved and how each is
  linked to the other two
• ?2 test

• Cat. Obs. No/ Phenotypes
  Genotypes ?2
• 29 yellow body y,e,f
• 25 yellow body, forked extra bristles
  y,e,f
• 28 forked extra bristles y,e,f
• 26 normal y,e,f
• 75 extra bristles y,e,f
• 74 yellow body, extra bristles y,e,f
• 72 forked bristles y,e,f
• 71 yellow body, forked bristles y,e,f
• Total 400

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Mapping exercise II

• Things to be considered to explain genetic
  linkage and mapping
• 3) Linkage determination -----gt three sets of two
  point mapping and ?2 test

• Cat. Obs. Genotypes y vs f ?2
• 29 y ,e,f 1 6
• 25 y ,e ,f 2 8
• 28 y,e ,f 3 7
• 26 y,e,f 4 5
• 75 y,e ,f
• 74 y ,e ,f
• 72 y,e,f
• 71 y ,e,f
• Total 400

Conclusion from ?2 -------gt
10
Mapping exercise II

• Things to be considered to explain genetic
  linkage and mapping
• 3) Linkage determination -----gt three sets of two
  point mapping and ?2 test

• Cat. Obs. Genotypes y vs e ?2
• 29 y ,e,f 1 8
• 25 y ,e ,f 2 6
• 28 y,e ,f 3 5
• 26 y,e,f 4 7
• 75 y,e ,f
• 74 y ,e ,f
• 72 y,e,f
• 71 y ,e,f
• Total 400

Conclusion from ?2 -------gt
11
Mapping exercise II

• Things to be considered to explain genetic
  linkage and mapping
• 3) Linkage determination -----gt three sets of two
  point mapping and ?2 test

• Cat. Obs. Genotypes e vs f ?2
• 29 y ,e,f 1 4
• 25 y ,e ,f 2 3
• 28 y,e ,f
• 26 y,e,f
• 75 y,e ,f 5 6
• 74 y ,e ,f
• 72 y,e,f 7 8
• 71 y ,e,f
• Total 400

Conclusion from ?2 -------gt
Genetic distance between e and f loci -------gt

12
Pedigree analysis (terminology)
Genetic analysis with family tree human
genetics
13
Pedigree analysis
Inheritance pattern of Huntingtons disease
----gt
14
Pedigree analysis

Inheritance pattern of Cystic fibrosis ----gt
15
Pedigree analysis

Inheritance pattern of X-chromosomal linked
diseases ----gt
16
Pedigree analysis

What about the following ones ----gt
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