Genetic Linkage and Mapping
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Summer placement students have studied the common vegetable fly (a diploid organism) and completed crosses of pure breeding flies with purple eyes (p), and vestigial (v; crinkled) wings to the commonly found red (P) eyed, normal winged (V) wild type flies.
The F1 offspring were all heterozygous wild type genotype.
Genotype
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1) Which answer from the list below is correct for the F1 offspring genotypes?
One answer only.
   all PpVv
   PPVv and ppVv
   PpVV and pPvv
   PpVV, pPvv, PPVv and ppVv
Gene Linkage
Crossing a female from the F1 with a male homozygous recessive for the traits gave the following phenotype results:
  1. Wild type eye, wild type wing = 1138 flies
  2. Wild type eye, vestigial wing = 150 flies
  3. Purple eye, wild type wing = 153 flies
  4. Purple eye, vestigial wing = 1194 flies
The offspring which have the same phenotype as the parents are called parental types, those which differ are called non-parental or recombinant types.
1) These results suggest that eye colour and wing shape here are linked, which statement supports this?
One answer only.
   Gene linkage produces equal numbers of offspring with parental and recombinant types
   Gene linkage produces a greater proportion of offspring with recombinant phenotypes (over parental types)
   Gene linkage produces a greater proportion of offspring with parental phenotypes (over recombinant types)
Map Distance
To calculate map distance you would take the number of recombinants (non-parental types) and divide by the total number of offspring, then multiply by 100.
1) Using the data above, which of the following is the correct sum?
One answer only.
   (1138 / (150+153 + 1194)) x 100
   ((150 + 153) / (1138 + 1194 + 150 + 153)) x 100
   ((150 + 153) / (1138 + 1194)) x 100
   ((1194) / (150 + 153 + 1138)) x 100
2) Which of the following is the correct sum?
One answer only.
   11.50
   13.00
   76.02
   82.86
Summary
In the above section we have looked at how to work out:
  1. the genotype for an organism
  2. determine whether or not genes are linked
  3. the map distance for genes
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