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Tree Genetics and Molecular Breeding 2012, Vol.2, No.1, 1
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microsatellites with three-base repeat would be made
clear differentiation in pine compared to the other two
species, and the proportion of microsatellites with
high polymorphism would be diminished accordingly.
Figure 1 The variation of repeat numbers for different types of EST-SSRs in pine, poplar and eucalyptus
Note: Pies indicated with A, B and C corresponding to pine, poplar and eucaplytus respectively. The numbers in brackets are the
repeat numbers of corresponding microsatellites. The percentage values stand for the proportion of microsatellites with certain repeat
numbers in the corresponding type of SSRs. In these figures, except for the first section with gray shadow, each section
corresponding to microsatellites with different number of repeat motif. In different types of microsatellites, the occurrence frequency
of very long microsatellites was low, long microsatellites with frequency lower than 1% were pooled in the first section with gray
shadow in each pie. The summed sections with gray shadow corresponding to the total amount of microsatellite with 20 bp or more
2 Discussions
Microsatellites widely distributed in eukaryotic genomes
(Ding and Tong, 1999). The latest studies have found
that microsatellites have many different functions,
such as affecting gene expression, regulation and
function. Compared to other sequences in the genome,
microsatellites have high frequency of variation that is
considered one important factor leading to generate
and maintain the variation of quantitative trait in the
process of genome evolution (Tautz et al., 1986; Kashi
et al., 1997). While a large number of studies had
found that instability of microsatellite closely related
to human cancer and neurological diseases (Lothe,
1997; Toth et al., 2000), such as microsatellite instability
leading to the incidence of breast cancer, colorectal
cancer, stomach cancer, prostate cancer, esophageal
cancer thyroid cancer etc. (Lin and Sun, 2003, Wujing
Yixueyuan Xuebao, 12(3): 231-233). Therefore, the
characteristics of microsatellite sequences would be
the important parameters to understand of the genome