Chapter 7 Outline

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Chapter 7 Outline

• 7.1 Linked Genes Do Not Assort Independently, 161
• 7.2 Linked Genes Segregate Together, and Crossing
  Over Produces Recombination between Them, 162
• 7.3 A Three-Point Testcross Can Be Used to Map
  Three Linked Genes, 175
• 7.4 Physical Mapping Methods Are Used to
  Determine the Physical Positions of Genes on
  Particular Chromosomes, 185
• 7.5 Recombination Rates Exhibit Extensive
  Variation, 188

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7.1 Linked Genes Do Not Assort Independently
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7.2 Linked Genes Segregate Together and Crossing
Over Produces Recombination between Them
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7.2 Linked Genes Segregate Together and Crossing
Over Produces Recombination between Them

• Notation for Crosses with Linkage
• Complete Linkage Leads to Nonrecombinant Gametes
  and Nonrecombinant Progeny
• Crossing Over with Linked Genes Lead to
  Recombiant Gametes and Recombinant Progeny

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Calculating Recombination Frequency

• Recombination frequency (number of recombinant
  progeny / total number of progeny) 100

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Coupling and Repulsion Configuration of Linked
Genes

• Coupling (cis configuration) Wild type alleles
  are found on one chromosome mutant alleles are
  found on the other chromosome.

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Coupling and Repulsion Configuration of Linked
Genes

• Repulsion (trans configuration) Wild-type allele
  and mutant allele are found on the same
  chromosome.

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Testing for Independent Assortment
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Concept Check 2
The following testcross produces the progeny
shown AaBb aabb ? 10 AaBb, 40 aaBb, 40 aaBb,
and 10 aabb. What is the percentage of
recombination between the A and B loci? Were the
genes in the AaBb parent in coupling or repulsion?
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Concept Check 2
The following testcross produces the progeny
shown AaBb aabb ? 10 AaBb, 40 aaBb, 40 aaBb,
and 10 aabb. What is the percent recombination
between the A and B loci? Were the genes in the
AaBb parent in coupling or repulsion?

• recombination 20 genes in the AaBb parent
  were in repulsion

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Gene Mapping with Recombination Frequencies

• Genetic maps are determined by recombinant
  frequency.
• Map unit and centiMorgans

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Constructing a Genetic Map with Two-Point
Testcrosses
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7.3 A Three-Point Testcross Can Be Used to Map
Three Linked Genes

• Constructing a Genetic Map with the Three-Point
  Testcross

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Constructing a Genetic Map with the Three-Point
Testcross

• Determining the gene order
• Determining the location of crossovers

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Concept Check 3
Write the genotypes of all recombinant and
nonrecombinant progeny expected from the
following three-point cross
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Concept Check 3
Write the genotypes of all recombinant and
nonrecombinant progeny expected from the
following three-point cross
Answer
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Concept Check 4
A three-point test cross is carried out between
three linked genes. The resulting nonrecombinant
progeny are src and s r c, and the
double-crossover progeny are s r c and src.
Which is the middle locus?
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Concept Check 4
A three-point test cross is carried out between
three linked genes. The resulting nonrecombinant
progeny are src and s r c, and the
double-crossover progeny are s r c and src.
Which is the middle locus?

• the C locus

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• Calculating the recombination frequencies
• Interference and coefficient of coincidence
• Effect of multiple crossovers
• Mapping human genes

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7.4 Physical Mapping Methods Are Used to
Determine the Physical Positions of Genes on
Particular Chromosomes

• Deletion Mapping
• Somatic Cell Hybridization

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