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If markers are randomly placed through the genome, then the average
distance between a QTL and the closest marker is
where
is the total map length and
is the number of markers
employed. The upper 95% confidence limit for the distance is
Since the human genome is 33M (3300cM), 110 random markers give an
average distance of 14.9cM and an upper 95% confidence limit
of 44.3cM, corresponding to recombination frequencies of 0.13 and
0.29, respectively. Since there are about 30,000 genes in the human
genome, there are roughly 10 genes per centimorgan. So if you're QTL
is 44cm from the nearest marker, there are probably over 400 genes in
the chromosomal segment you've identified.
If
is the recombination fraction between the nearest marker
locus and the QTL of interest, the frequency of recombinant genotypes
among
progeny is
. As you can see
from the graph in Figure 1, there's a nearly
linear relationship between recombination frequency and the frequency
of recombinant phenotypes (
in the graph).
Figure 1:
The relationship between recombination frequency,
, and
the frequency of recombinant phenotypes,
, assuming a Haldane
mapping function.
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Next: Analysis of an derived
Up: Mapping quantitative trait loci
Previous: Genetic recombination and mapping
Kent Holsinger
2008-09-02