Learning Objective

Know how to write genotypes using linkage nomenclature
Know the the 2 P-gen crossing options for setting up a dihybrid
- WT x double-mutant (AABB x aabb)
- single mutant x single mutant (AAbb x aaBB)
Know that the linkage analysis cross is: dihybrid x test (AaBb x aabb)
- recognize that the test cross is also used for determining unknown genotypes (from prev lectures)
Know which class are parental (non-recombinant) and non-parental (recombinant) from your P-gen setup
- WT x double Pgen -> parentals are WT & double
- single x single Pgen -> single & other single are parentals
Know that the 2 smaller ratio are (pretty much) always the non-parentals
Know that recombination is reciprocal and therefore we always get equal ratios of:
- the 2 classes of parentals
- the 2 classes of non-parentals
Know what the results of linkage analysis indicate
- uneven ratios (X:X:1:1) = linked
- 1:1:1:1 = unlinked OR linked by far apart
Be able to calculate distance
- # non-parentals / total (sum 2 smaller numbers / total)
- Distance = recombination frequency
- = % = cM
Given distance be able to predict relative distribution of classes
- ex: if distance is 30cM and there are 1000 progeny,
  then 30% or 300 are non-parentals.
  so 150:150 non-parentals 350:350 parentals
Given gene distances, be able to create a cytogenetic map
understand that in mutagenesis is rare, so if in drosophila, a mutation is given (aa), that all other traits are homozygous for wt (BB, DD, EE etc)
Understand that the purpose of the complementation is to determine if two observed mutant with the same phenotype are due to 1 gene or 2 different genes that just happen to have the same phenotype.
Know that the complementation test is to mate 2 similar appearing mutants to each other
Know what the outcomes of the complementation test indicate
- If all progeny are mutant --> then mutants are in the same gene
- If all progeny are WT --> then mutants are in different genes

Additional Terms

WT (wild-type)
double mutant
single mutant
crossing-over
to type out linkage nomenclatures:
- Linked AB/ab
- unlinked A/a B/B

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The specific mechanism (how) of homologous recombination is quite interesting and complicated. Below are 2 short video explaining the process. They explore a process involving something called a Holliday junction, however, there are other mechanisms.

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