Geoscience Reference
In-Depth Information
(http://iasri.res.in/ebook/EB_SMAR/e-book_pdf%20files/
Manual%20IV/10-QTL.pdf).
The principle behind the QTL mapping implicates par-
titioning the mapping population into different genotypic
groups based on the genotype data on the mapping population
for determining whether significant differences exist between
groups with respect to the trait being measured (Tanksley
1993; Young 1996). A major dissimilarity between phenotypic
means of the groups (either 2 or 3), depending on the marker
system and type of population, indicates that the marker locus
being used to partition the mapping population is linked to a
QTL controlling the trait. The P value obtained from the dif-
ferences between mean trait values indicates linkage between
marker and QTL and is due to recombination. The diagram
representing the linkage between marker and QTL are
Marker E
Marker H
123456789101112131415161718 19 20
12345678910 11 12 13 14 15 16 17 18 19 20
AABB
AAA A AA AAA
31 40 38 28 43 32 40 30 39 42 28 30 29 41 31 30 32 40 39
BBBB
B
B
B
ABBA
BBA B AA BAA
31 40 38 28 43 32 40 30 39 42 28 30 29 41 31 30 32 40 39
BBAB
A
B
A
33
33
Group 1 (progeny
with fragment A)
Group 2 (progeny
with fragment B)
Group 1 (progeny
with fragment A)
Group 2 (progeny
with fragment B)
50
50
40
30
20
10
0
40
30
20
10
0
AB
AB
Marker E genotype
Marker H genotype
P value <0.0001 = Significant
P value 0.5701 = Not significant
Conclusion: Marker is linked to a QTL
Conclusion: Marker is unlinked to a QTL
FIGURe 17.4 Principle of qTL mapping. Markers that are linked to a gene or qTL
controlling a particular trait (e.g. plant height) will indicate significant differences
when the mapping population is partitioned according to the genotype of the
marker. Based on the results in this diagram, Marker E is linked to a qTL because
there is a significant difference between means. Marker H is unlinked to a qTL
because there is no significant difference between means. The closer the marker
is to the qTL of interest, the lower the chance for recombination between marker
and qTL. (Adapted from Collard, B. C. Y., Jahufer, M. Z. Z., Brouwer, J. B., and
Pang, E. C. K. 2005. Euphytica , 142(1-2), 169-196.)
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