Plant Genome I Conference
Town & Country Conference Center, San Diego, CA, November, 1992.
PG-I: MAPPING QUANTITATIVE TRAIT LOCI IN RANDOM MATING POPULATIONS
MAPPING QUANTITATIVE TRAIT LOCI IN RANDOM MATING POPULATIONS.
Thomas Mitchell-Olds, Division of Biological Sciences, University
of Montana, Missoula, MT 59812.
Mapping quantitative trait loci (QTLS) in forest trees is
complicated by their outcrossed, genetically variable population
structure. Although interval mapping methods have been applied
to crosses between inbred lines, this procedure has not been
available for studies of tree populations. We have extended
maximum likelihood interval mapping methods to accommodate
crosses among heterozygous parents with multiple alleles per
locus. I will discuss the conceptual basis and practical
application of interval mapping for forest genetics researchers.
Briefly, the likelihood of an observation is the probability of
obtaining one's observations given a particular statistical
model. The method of maximum likelihood finds the statistical
estimates that best fit the data (that maximize the likelihood).
At each point in the genome, we calculate the likelihood that a
QTL is or is not present, given information from nearby molecular
markers. Interval mapping is valuable for a sparse molecular
map, since it allows inferences about QTLs within an interval,
between markers. As maps improve and markers become closely
spaced, then most QTL mapping methods produce equivalent results.
Complicating factors in outcrossed populations, such as multiple
alleles per locus and unknown linkage phase, may also be
discussed.
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