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7. ROLE OF QTLs IN THE EARLY EVOLUTION...
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7.3.4. Genomic distribution of QTLs in L. multiflorum and L. perenne
QTLs were located among all linkage groups (Figure 7.6 A-G). Unsurprisingly, a little
more QTLs were detected on longer linkage groups (Table 7.6) than on shorter. The similar
tendency was observed for major QTLs. The mean phenotypic variance explained by all
QTLs located on different linkage groups was very alike. Nevertheless, a QTL size depended
on a linkage group and the biggest QTLs were located on the three longest groups i.e., LG1
(214.2 cM), LG2 (183.7 cM) and LG4 (164.1 cM). In general the mean LOD value was similar
for the majority of linkage groups. The only exceptions were LG3 and LG6 for which mean
LOD values were significantly higher. This result was attributable to QTLs responsible for the
presence of awns and days from spring rush to ear emergence that had extremely high LOD
values. In addition, the QTL for basal leaf length with LOD value equal to 45.5 was detected
on LG3.
Densities of QTLs calculated as a number of QTLs per 1 cM were somehow different on
each linkage group and they were not correlated with LG length. Indeed, the highest density
was exhibited by groups of modest length as LG6 and LG3. Visual inspection of QTLs’ map
positions demonstrated clearly some level of overlapping (Figure 7.6 A-G). A good measure
of overlapping was obtained if the total length of all QTLs on a given linkage group was
divided by the LG length (Figure 7.7). The obtained value that could be described as a coefficient
of overlapping showed the highest number of QTLs occupying the similar position on
LG4. As many as five QTLs shared the same position and this calculation was in agreement
with the visual inspection. Notwithstanding the fact that the lowest overlapping was found
on the shortest linkage group, LG7, no correlation was observed between the linkage group
length and the level of overlapping. Somehow lower overlapping was found for major QTLs
but it simply resulted from fewer major QTLs.
In some cases overlapping QTLs shared exactly the same position concerning flanking
markers and markers linked with them at maximum LOD value. In these cases, it was
reasonable to speculate that overlapping QTLs represented the same genes with pleiotropic
effect. This must have been true for QTLs controlling green and dry weight of tillers on LG2
and LG4, green and dry weight of vegetative part on LG3 and basal leaf width and area on
LG3. In other cases, despite QTLs spanned over the same distance, the linked markers with
the highest LOD value were quite different. Although pleiotropy could not be excluded, the