Genomics and Applied Biology 2018, Vol.9, No.4, 19-23
21
method was 1.68317 times higher than that based on AELP method; Population specific
Fst
based on SSR was
1.24987 times higher than that based on AELP; Average genetic diversity index in population was 1.67660 times
higher than that based on AELP. The results of this study could provide methods and reference for other similar
research. The results of this study provided the basis for population genetic diversity assessment, and researchers
could estimate the results of genetic diversity studies using one of the SSR or AFLP methods based on this ratio.
Jiang et al. (2007) compared the genetic diversity in peanut genotypes with bacterial wilt resistance through SSR
and AELP technique, and found that SSR analysis showed the genetic distance of 31 peanut genotypes ranged
from 0.12 to 0.94, with an average of 0.53. The genetic distance of the 31 peanut genotypes obtained by AELP
ranged from 0.06 to 0.57, with an average of 0.25. In this study, the ratio of genetic distance among 5 selected
populations calculated by SSR method and AFLP method was in the range of 2.824 10 and 6.92063, with an
average of 3.97202 (Nei, 1972), whereas the ratio of genetic identity was between 0.928 10 and 0.945 45, with an
average of 0.937 92 (Nei, 1972). This study showed that the genetic distance between populations based on SSR
analysis was greater than that based on AFLP analysis, which was consistent with the results of Jiang (2007). As
for the detailed ratio, the average genetic distance obtained by Jiang (2007) based on SSR was 2.12 times of that
obtained by AFLP, which less than the ratio 3.97202 in this study. The difference was mainly related to the genetic
relationship between populations, as well as the technical characteristics of the two markers. The object of this
study was 5 populations of
Nile tilapia
, and it was known that relationship among populations closely. The
research object of Jiang (2007) was 31 cultivated peanut genotypes materials with different resistance to bacterial
wilt. Therefore, there was a great difference between genetic distance and genetic identity among populations.
About the characteristics of molecular marking techniques, AELP was aimed at restriction endonuclease fragment
from the entire genome, selective amplification with different primer combinations. The genetic diversity of the
detection was the change of the restriction site in the genome or the variation of the DNA sequence length in the
enzyme fragment. This result was reliable and stable (Wang et al., 2006). Essentially, SSR is a simple repeat
sequence scattered in the eukaryote genomes, mainly distributed in the non-coding region. Because of the
different base composition of repeat sequence, and the range of variation of repeat number is very large, it shows
high polymorphism. However, SSR sequences are easily influenced by convergent variation and parallel evolution
during biological evolution, which bring errors to the analysis of genetic relationships in the assessment of genetic
diversity (Xu and Wang, 2001). Therefore, molecular markers used in the analysis of genetic distance and genetic
identity among populations should be carefully selected according to the genetic relationships between materials.
In the aspect of horizontal comparison and evaluation of the results, the study of genetic diversity ratio in
SSR/AFLP population has a good reference value.
3 Materials and Methods
3.1 Experiment materials
Team of Professor Li Sifa from Shanghai Ocean University introduced 5, 000
Oreochromis niloticus
in 1994,
which was used as a base group (F0). Since 1996, the system breeding of superior species has been carried out,
and a new generation of selective breeding population has been produced every year. Each generation was marked
as F
1
~F
9
. Experiment materials
of
this study were selected from 5 generations of reserved F
0
, F6~F9 for breeding
of superior species of
Oreochromis niloticus
. Selected 20 samples
from each generation randomly, cut tissue of
caudal fin, numbered respectively, and then preserved with 95% ethanol for DNA extraction (Xie et al., 2011)
.
3.2 Molecular marker analysis
3.2.1 DNA extraction
The DNAs of 100 individuals were extracted from 5 generations of experimental materials by routine
phenol/chloroform extracting method. Then agarose gel electrophoresis was used to detect the extracted DNA
samples.
3.2.2 Reaction system and program of SSR and AFLP
In this study, the total volume of liquid in the SSR reaction system was 25 μL, which contained about 50 ng
genomic DNA, 3 μL buffer solution (10 mmol/LTris-HCl, pH9.0, 50 mmol/LKCl, 3.0 mmol/LMgCl
2
, and 0.001%
