Recombinants
new associations of parental alleles produced by genetic recombination
How do we determine if two genes are linked?
testcrosses, and a linkage map is constructed
syntenic genes
genes on the same chromosome
complete genetic linkage
genes are located so close together on the same chromosome that they are virtually never separated by crossing over
How are linked genes found?
by looking for deviation from the expected frequencies of indpendent assortment
Interference
crossovers appear to reduce formation of other chiasmata (crossovers) nearby
if interference = 1, there are no other crossovers in the region
Equation for interference
1 - coefficient of coincedence (# of observed double recombinants / number of expected double recombinants)
LOD score
a statistical measure used to determine the probability that two genes or genetic markers are located close together on a chromosome and are therefore likely to be inherited together
LOD score of 3 or higher
strong evidence for linkage
negative LOD score
loci are unlinked
recombination frequency (r) equation
(# of recombinants)/(total number of progeny)
positively correlated with physical distance between two genes
LOD score equation
log 10 (probability that the two loci are linked/probability that the two loci are not linked)
Allelic phase
which alleles are physically attached to each other on the same chromosome
important because disease-causing genes are identified by identifying linked polymorphisms
