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1.
Due to a high evolutionary turnover many satellite DNAs are restricted to a group of closely related species. Here we demonstrate
that the satellite DNA family PSUB, abundant in the beetle Palorus subdepressus, is distributed in a low number of copies among diverse taxa of Coleoptera (Insecta), some of them separated for an evolutionary
period of up to 60 Myr. Comparison of PSUB cloned from the species Tribolium brevicornis with the PSUB family previously characterized in Palorus subdepressus revealed high sequence conservation and absence of fixed species-specific mutations. The most polymorphic sites are those
with ancestral mutations shared among clones of both species. Since the ancestral mutations contribute significantly to overall
diversity, it could be proposed that a similar mutational profile already existed in an ancestral species. The pattern of
variability along the satellite monomer is characterized by the presence of conserved and variable regions. The nonrandom
pattern of variability as well as the absence of sequence divergence is also discerned for PRAT satellite DNA, cloned previously
from two Palorus species and a distantly related Pimelia elevata. Since PRAT and PSUB are present in parallel in diverse taxa of Coleoptera, we propose that their long evolutionary preservation
suggests a possible functional significance. This indication is additionally supported not only by the high evolutionary conservation
of the sequences, but also by the presence of significantly conserved and variable regions along the monomers.
[Reviewing Editor: Dr. Jerzy Jurka] 相似文献
2.
Miroslav Plohl Nevenka Mestrović Branka Bruvo Đurđica Ugarković 《Journal of molecular evolution》1998,46(2):234-239
A novel highly abundant satellite DNA comprising 20% of the genome has been characterized in Palorus subdepressus (Insecta, Coleoptera). The 72-bp-long monomer sequence is composed of two copies of T2A5T octanucleotide alternating with 22-nucleotide-long elements of an inverted repeat. Phylogenetic analysis revealed clustering
of monomer sequence variants into two clades. Two types of variants are prevalently organized in an alternating pattern, thus
showing a tendency to generate a new complex repeating unit 144 bp in length. Fluorescent in situ hybridization revealed even
distribution of the satellite in the region of pericentric heterochromatin of all 20 chromosomes. P. subdepressus satellite sequence is clearly species specific, lacking similarity even with the satellite from congeneric species P. ratzeburgii. However, on the basis of similarity in predicted tertiary structure induced by intrinsic DNA curvature and in repeat length,
P. subdepressus satellite can be classified into the same group with satellites from related tenebrionid species P. ratzeburgii, Tenebrio molitor, and T. obscurus. It can be reasonably inferred that repetitive sequences of different origin evolve under constraints to adopt and conserve
particular features. Obtained results suggest that the higher-order structure and repeat length, but not the nucleotide sequence
itself, are maintained through evolution of these species.
Received: 23 April 1997 / Accepted: 11 July 1997 相似文献
3.
Very abundant and homogenous satellite DNA has been found in the flour beetle Palorus ratzeburgii, representing 40% of its genome. Sequencing of 14 randomly cloned satelite monomers revealed a conserved monomer length of 142 bp and an average A+T content of 68%. Sequence variation analysis showed that base substitutions, appearing with a frequency of 2.3%, are predominant differences among satellite monomers. The satellite sequence is unique without significant direct repeats and with only two potentially stable inverted repeats. After electrophoresis of satellite monomers on native polyacrylamide gel retarded mobilities characteristic for curved DNA molecules are observed. The curvature profiles and DNA helix axis trajectory are calculated on the basis of three different algorithms. These calculations predict that P ratzeburgii satellite DNA forms a left-handed solenoid superstructure. Comparison of described features with other satellite DNAs reveals some striking similarities with satellite DNA from related species Tenebrio molitor, which belongs to the same family of Tenebrionidae. Both satellites are very abundant and homogenous with the same, highly conserved monomer length, although there is no homology at the nucleotide level. Their monomers, as well as multimers, exhibit very similar retarded electrophoretic mobilities. The calculated curvature profiles predict two bend centers in monomers of each satellite, resulting in a model of left-handed solenoid superstructures of similar appearance. 相似文献
4.
Philippe Castagnone-Sereno Hélène Leroy Jean-Philippe Semblat Frédéric Leroy Pierre Abad Carolien Zijlstra 《Journal of molecular evolution》1998,46(2):225-233
An AluI satellite DNA family has been isolated in the genome of the root-knot nematode Meloidogyne chitwoodi. This repeated sequence was shown to be present at approximately 11,400 copies per haploid genome, and represents about 3.5%
of the total genomic DNA. Nineteen monomers were cloned and sequenced. Their length ranged from 142 to 180 bp, and their A
+ T content was high (from 65.7 to 79.1%), with frequent runs of As and Ts. An unexpected heterogeneity in primary structure
was observed between monomers, and multiple alignment analysis showed that the 19 repeats could be unambiguously clustered
in six subfamilies. A consensus sequence has been deduced for each subfamily, within which the number of positions conserved
is very high, ranging from 86.7% to 98.6%. Even though blocks of conserved regions could be observed, multiple alignment of
the six consensus sequences did not enable the establishment of a general unambiguous consensus sequence. Screening of the
six consensus sequences for evidence of internal repeated subunits revealed a 6-bp motif (AAATTT), present in both direct
and inverted orientation. This motif was found up to nine times in the consensus sequences, also with the occurrence of degenerated
subrepeats. Along with the meiotic parthenogenetic mode of reproduction of this nematode, such structural features may argue
for the evolution of this satellite DNA family either (1) from a common ancestral sequence by amplification followed by mechanisms
of sequence divergence, or (2) through independent mutations of the ancestral sequence in isolated amphimictic nematode populations
and subsequent hybridization events. Overall, our results suggest the ancient origin of this satellite DNA family, and may
reflect for M. chitwoodi a phylogenetic position close to the ancestral amphimictic forms of root-knot nematodes.
Received: 23 April 1997 / Accepted: 9 July 1997 相似文献
5.
Mutation and Recombination in Cattle Satellite DNA: A Feedback Model for the Evolution of Satellite DNA Repeats 总被引:6,自引:0,他引:6
The cattle genome contains several distinct centromeric satellites with interrelated evolutionary histories. We compared
these satellites in Bovini species that diverged 0.2 to about 5 Myr ago. Quantification of hybridization signals by phosphor imaging revealed a large
variation in the relative amounts of the major satellites. In the genome of water buffalo this has led to the complete deletion
of satellite III. Comparative sequencing and PCR-RFLP analysis of satellites IV, 1.711a, and 1.711b from the related Bos and Bison species revealed heterogeneities in 0.5 to 2% of the positions, again with variations in the relative amounts of sequence
variants. Restriction patterns generated by double digestions suggested a recombination of sequence variants. Our results
are compatible with a model of the life history of satellites during which homogeneity of interacting repeat units is both
cause and consequence of the rapid turnover of satellite DNA. Initially, a positive feedback loop leads to a rapid saltatory
amplification of homogeneous repeat units. In the second phase, mutations inhibit the interaction of repeat units and coexisting
sequence variants amplify independently. Homogenization by the spreading of one of the variants is prevented by recombination
and the satellite is eventually outcompeted by another, more homogeneous tandem repeat sequence.
Received: 21 July 2000 / Accepted: 30 October 2000 相似文献
6.
Chromosome terminal, complex repeats in the dipteran Chironomus pallidivittatus show rapid concerted evolution during which there is remarkably efficient homogenization of the repeat units within and between
chromosome ends. It has been shown previously that gene conversion is likely to be an important component during these changes.
The sequence evolution could be a result of different processes—exchanges between repeats in the tandem array as well as information
transfer between units in different chromosomes—and is therefore difficult to analyze in detail. In this study the concerted
evolution of a region present only once per chromosome, at the junction between the telomeric complex repeats and the subtelomeric
DNA was therefore investigated in the two sibling species C. pallidivittatus and C. tentans. Material from individual microdissected chromosome ends was used, as well as clones from bulk genomic DNA. On the telomeric
side of the border pronounced species-specific sequence differences were observed, the patterns being similar for clones of
different origin within each species. Mutations had been transmitted efficiently between chromosomes also when adjoining,
more distally localized DNA showed great differences in sequence, suggesting that gene conversion had taken place. The evolving
telomeric region bordered proximally to subtelomeric DNA with high evolutionary constancy. More proximally localized, subtelomeric
DNA evolved more rapidly and showed heterogeneity between species and chromosomes.
Received: 24 September 1997 / Accepted: 24 November 1997 相似文献
7.
A family of four satellite DNAs has been characterized in the genome of the bivalve mollusc, Donax trunculus. All share HindIII sites, a similar monomer length of about 160 base pairs (bp), and the related oligonucleotide motifs GGTCA and GGGTTA,
repeated six to 15 times within the repetitive units. The motif GGTCA is common to all members of the satellite family. It
is present in three of them in both orientations, interspersed within nonrepetitive DNA sequences. The hexanucleotide GGGTTA
appears to be the main building element of one of the satellites forming a prominent subrepeat structure in conjunction with
the 5-bp motif. The former has been also found in perfect tandem repeats in a junction region adjacent to the proper satellite
sequence. Southern analysis has revealed that (GGGTTA)n and/or related sequences are abundant and widely distributed in the D. trunculus genome. The distribution observed is consistent with the concurrence of the scattering of short sequence motifs throughout
the genome and the spread of longer DNA segments, with concomitant formation of satellite monomer repeats. Both kinds of dispersion
may have contributed to the observed complex arrangement of the HindIII satellite DNA family in Donax.
Received: 28 May 1996 / Accepted: 30 July 1996 相似文献
8.
9.
Telomeres of most insects are composed of simple (TTAGG)
n
repeats that are synthesized by telomerase. However, in some dipteran insects such as Drosophila melanogaster, (TTAGG)
n
repeats or telomerase activity has not been detected. Although telomere structure is well documented in Diptera and Lepidoptera,
very limited information is available on lower insect groups. To understand general aspects of telomere function and evolution
in insects, we endeavored to characterize structures of the telomeric and subtelomeric regions in a lower insect, the Taiwan
cricket, Teleogryllus taiwanemma. FISH analysis of this insect's chromosomes demonstrated (TTAGG)
n
repeat elements in all distal ends. Just proximal to the telomeric repeats, the highly conserved 9-kb long terminal unit
(LTU) sequences are tandemly repeated. These were observed in four of six chromosomes, three autosomal ends, and one X-chromosomal
end. LTU sequences represent about 0.2% of the T. taiwanemma genome. Each LTU contains a core (TTAGG)8-like sequence (TRLS) and five types of conserved sequences—ST (short telomere associated), J (joint), X, SR (satellite sequence
rich), and Y—which vary in length from about 150 bp to 2.7 kb. The LTU sequence is defined as ST–J–TRLS–SR–X–Y–X–Y–X. Most
LTU regions may be derived from the ancestral common sequence, which is observed in ST regions six times and at many other
LTU sites. We could not find the LTU-like sequence in three other crickets including the closest species, T. emma, suggesting that the LTU in T. taiwanemma has been rapidly amplified in subtelomeric regions through recent evolutional events. It is also suggested that the highly
conserved structure of the LTU is maintained by recombination and may contribute to telomere elongation, as seen in dipteran
insects.
Received: 6 August 2001/Accepted: 10 October 2001 相似文献
10.
Major satellites of species in the genus Pimelia comprise large portions of their genomes and belong to seven major satellite families which all originate from a common ancestral
sequence. Here we present the results of comprehensive screening of 26 Pimelia species belonging to three distinct geographic groups (Ibero-Balearic, African and Canary Islands) for the presence of different
Pimelia satellite families in their genomes. Dot-blot hybridization experiments suggest that together with one dominant, highly abundant
satellite family, other families are also present in genomes of the majority of examined Pimelia species, but as low-copy number repeats. The estimated abundance of these underrepresented repeats is about 4,000 copies
per haploid genome. Signals of highly abundant satellite family from P. scabrosa (PSCA) in examined congeneric species, obtained after PCR amplification and Southern hybridization under high stringency
conditions, corroborate sequence preservation of low-copy representatives of satellite families. PRINS localized low-copy
repeats within the pericentromeric regions of all chromosomes. These results point to the existence of an extensive library
of repetitive DNAs that was already present in the genome of the common ancestor of extant Pimelia taxa, and shifts the period of diversification of Pimelia satellites far in the history of this genus. 相似文献
11.
Sybille Kubis John Seymour Heslop-Harrison Thomas Schmidt 《Journal of molecular evolution》1997,44(3):310-320
Members of a highly abundant restriction satellite family have been isolated from the wild beet species Beta nana. The satellite DNA sequence is characterized by a conserved RsaI restriction site and is present in three of four sections of the genus Beta, namely Nanae, Corollinae, and Beta. It was not detected in species of the evolutionary old section Procumbentes, suggesting its amplification after separation of this section. Sequences of eight monomers were aligned revealing a size
variation from 209 to 233 bp and an AT content ranging from 56.5% to 60.5%. The similarity between monomers in B. nana varied from 77.7% to 92.2%. Diverged subfamilies were identified by sequence analysis and Southern hybridization. A comparative
study of this repetitive DNA element by fluorescent in situ hybridization and Southern analyses in three representative species
was performed showing a variable genomic organization and heterogeneous localizations along metaphase chromosomes both within
and between species. In B. nana the copy number of this satellite, with some 30,000 per haploid genome, is more than tenfold higher than in Beta lomatogona and up to 200 times higher than in Beta vulgaris, indicating different levels of sequence amplification during evolution in the genus Beta. In sugar beet (B. vulgaris), the large-scale organization of this tandem repeat was examined by pulsed-field gel electrophoresis. Southern hybridization
to genomic DNA digested with DraI demonstrated that satellite arrays are located in AT-rich regions and the tandem repeat is a useful probe for the detection
of genetic variation in closely related B. vulgaris cultivars, accessions, and subspecies.
Received: 24 May 1996 / Accepted: 13 September 1996 相似文献
12.
Charles Lee Dean R. Court Charles Cho Jennifer L. Haslett Chyi-Chyang Lin 《Journal of molecular evolution》1997,44(3):327-335
Based on sequence analyses of 17 complete centromeric DNA monomers from ten different deer species, a model is proposed for
the genesis, evolution, and genomic organization of cervid satellite I DNA. All cervid satellite I DNA arose from the initial
amplification of a 31-bp DNA sequence. These 31-bp subrepeats were organized in a hierarchical fashion as 0.8-kb monomers
in plesiometacarpalia deer and 1-kb monomers in telemetacarpalia deer. The higher-order repeat nature of cervid centromeric
satellite DNA monomers accounts for their high intragenomic and intraspecific sequence conservation. Such high intraspecific
sequence conservation validates the use of a single cervid satellite I DNA monomer from each deer species for interspecific
sequence comparisons to elucidate phylogenetic relationships. Also, a specific 0.18-kb tandem duplication was observed in
all 1-kb monomers, implying that 1-kb cervid satellite I DNA monomers arose from an unequal crossover event between two similar
0.8-kb ancestral DNA sequences.
Received: 28 May 1996 / Accepted: 24 October 1996 相似文献
13.
Ewa Ziętkiewicz Chantal Richer Daniel Sinnett Damian Labuda 《Journal of molecular evolution》1998,47(2):172-182
To get insight into the early evolution of the primate Alu elements, we characterized sequences of these repeats from the
Malagasy prosimians, lemurs (Lemuridae) and sifakas (Indriidae), as well as from galagos (Lorisidae). These sequences were
compared with the oldest Alu species known from the human genome: dimeric Alu J and S and free Alu monomers. Our analysis
indicates that about 60 Myr ago, before the prosimian divergence, free left and right monomers formed an Alu heterodimer connected
by a 19-nucleotide-long A-rich linker. The resulting elements successfully propagated in diverging primate lineages until
about ∼20 Myr ago, conserving similar sequence features and essentially the same Alu RNA secondary structure. We suggest that
until that time the same ``retropositional niche', molecular machinery making possible the proliferation by retroposition,
constrained the evolution of Alu elements in extant primate species. These constraints became subsequently relaxed. In the
Malagasy prosimians the dimeric Alu continued to amplify after acquiring a 34- to 36-nucleotide extension of their linker
segment, whereas in the galago genome the ``retropositional niche' was occupied by novel short elements.
Received: 1 December 1997 / Accepted: 30 January 1998 相似文献
14.
The complete mitochondrial DNA (mtDNA) of the donkey and mtDNA comparisons among four closely related mammalian species-pairs 总被引:7,自引:0,他引:7
The nucleotide sequence of the complete mitochondrial genome of the donkey, Equus asinus, was determined. The length of the molecule is 16,670 bp. The length, however, is not absolute due to pronounced heteroplasmy
caused by variable numbers of two types of repetitive motifs in the control region. The sequence of the repeats is (a) 5′-CACACCCA
and (b) 5′-TGCGCGCA, respectively. The order of (a) and (b) can be expressed as {n[2(a)+(b)]+m(a)}. In 32 different clones analyzed the number of n and m ranged from 0 to 9 and 1 to 7. The two rRNA genes, the 13 peptide-coding genes, and the 22 tRNA genes of the donkey and the
horse, Equus caballus, were compared in detail. Total nucleotide difference outside the control region was 6.9%. Nucleotide difference between peptide-coding
genes ranged from 6.4% to 9.4% with a mean of 8.0%. In the inferred protein sequences of the 13 peptide-coding genes the amino
acid difference was 0.2–8.8%, and the mean for the 13 concatenated amino acid sequences was 1.9%. In the 22 tRNA genes, the
mean difference was 3.5%, and that in the two rRNA genes was 4.1%. The mtDNA differences between the donkey and the horse
suggest that the evolutionary separation of the two species occurred ≈9 million years ago. Analyses of differences among the
mtDNAs of three other species-pairs, harbor seal/grey seal, fin whale/blue whale, and Homo/common chimpanzee, showed that the relative evolutionary rate of individual peptide-coding genes varies among different species-pairs
and modes of comparison. The findings show that the superimposition of sequence data of one lineage for resolving and dating
evolutionary divergences of other lineages should be performed with caution unless based on comprehensive data.
Received: 15 October 1995 / Accepted: 15 April 1996 相似文献
15.
Diversity, Distribution, and Ancient Taxonomic Relationships Within the TIR and Non-TIR NBS-LRR Resistance Gene Subfamilies 总被引:1,自引:0,他引:1
Cannon SB Zhu H Baumgarten AM Spangler R May G Cook DR Young ND 《Journal of molecular evolution》2002,54(4):548-562
Phylogenetic relationships among the NBS-LRR (nucleotide binding site–leucine-rich repeat) resistance gene homologues (RGHs)
from 30 genera and nine families were evaluated relative to phylogenies for these taxa. More than 800 NBS-LRR RGHs were analyzed,
primarily from Fabaceae, Brassicaceae, Poaceae, and Solanaceae species, but also from representatives of other angiosperm
and gymnosperm families. Parsimony, maximum likelihood, and distance methods were used to classify these RGHs relative to
previously observed gene subfamilies as well as within more closely related sequence clades. Grouping sequences using a distance
cutoff of 250 PAM units (point accepted mutations per 100 residues) identified at least five ancient sequence clades with
representatives from several plant families: the previously observed TIR gene subfamily and a minimum of four deep splits
within the non-TIR gene subfamily. The deep splits in the non-TIR subfamily are also reflected in comparisons of amino acid
substitution rates in various species and in ratios of nonsynonymous-to-synonymous nucleotide substitution rates (K
A/K
S values) in Arabidopsis thaliana. Lower K
A/K
S values in the TIR than the non-TIR sequences suggest greater functional constraints in the TIR subfamily. At least three
of the five identified ancient clades appear to predate the angiosperm–gymnosperm radiation. Monocot sequences are absent
from the TIR subfamily, as observed in previous studies. In both subfamilies, clades with sequences separated by approximately
150 PAM units are family but not genus specific, providing a rough measure of minimum dates for the first diversification
event within these clades. Within any one clade, particular taxa may be dramatically over- or underrepresented, suggesting
preferential expansions or losses of certain RGH types within particular taxa and suggesting that no one species will provide
models for all major sequence types in other taxa.
Received: 13 June 2001 / Accepted: 22 October 2001 相似文献
16.
17.
Cristina M. Justice Zhining Den Son V. Nguyen Mark Stoneking Prescott L. Deininger Mark A. Batzer Bronya J.B. Keats 《Journal of molecular evolution》2001,52(3):232-238
Friedreich ataxia is an autosomal recessive neurodegenerative disorder associated with a GAA repeat expansion in the first
intron of the gene (FRDA) encoding a novel, highly conserved, 210 amino acid protein known as frataxin. Normal variation in
repeat size was determined by analysis of more than 600 DNA samples from seven human populations. This analysis showed that
the most frequent allele had nine GAA repeats, and no alleles with fewer than five GAA repeats were found. The European and
Syrian populations had the highest percentage of alleles with 10 or more GAA repeats, while the Papua New Guinea population
did not have any alleles carrying more than 10 GAA repeats. The distributions of repeat sizes in the European, Syrian, and
African American populations were significantly different from those in the Asian and Papua New Guinea populations (p < 0.001). The GAA repeat size was also determined in five nonhuman primates. Samples from 10 chimpanzees, 3 orangutans, 1
gorilla, 1 rhesus macaque, 1 mangabey, and 1 tamarin were analyzed. Among those primates belonging to the Pongidae family,
the chimpanzees were found to carry three or four GAA repeats, the orangutans had four or five GAA repeats, and the gorilla
carried three GAA repeats. In primates belonging to the Cercopithecidae family, three GAA repeats were found in the mangabey
and two in the rhesus macaque. However, an AluY subfamily member inserted in the poly(A) tract preceding the GAA repeat region in the rhesus macaque, making the amplified
sequence approximately 300 bp longer. The GAA repeat was also found in the tamarin, suggesting that it arose at least 40 million
years ago and remained relatively small throughout the majority of primate evolution, with a punctuated expansion in the human
genome.
Received: 18 August 2000 / Accepted: 10 November 2000 相似文献
18.
We examined the evolution of the repeat regions of three noncoding microsatellite loci in 58 species of the Polistinae, a
subfamily of wasps that diverged over 140 million years ago. A phylogenetic approach allows two new kinds of approaches to
studying microsatellite evolution: character mapping and comparative analysis. The basic repeat structure of the loci was
highly conserved, but was often punctuated with imperfections that appear to be phylogenetically informative. Repeat numbers
evolved more rapidly than other changes in the repeat region. Changes in number of repeats among species seem consistent with
the stepwise mutation model, which is based on slippage during replication as the main source of mutations. Changes in repeat
numbers can occur even when there are very few tandem repeats but longer repeats, especially perfect repeats led to greater
rates of evolutionary change. Species phylogenetically closer to the one from which we identified the loci had longer stretches
of uninterrupted repeats and more different motifs, but not longer total repeat regions. The number of perfect repeats increased
more often than it decreased. However, there was no evidence that some species have consistently greater numbers of repeats
across loci than other species have, once ascertainment bias is eliminated. We also found no evidence for a population size
effect posited by one form of the directionality hypothesis. Overall, phylogenetic variation in repeat regions can be explained
by adding neutral evolution to what is already known about the mutation process. The life cycle of microsatellites appears
to reflect a balance between growth by slippage and degradation by an essentially irreversible accumulation of imperfections.
Received: 13 April 1999 / Accepted: 8 September 1999 相似文献
19.
Tandemly repeated sequences are a major component of the eukaryotic genome. Although the general characteristics of tandem
repeats have been well documented, the processes involved in their origin and maintenance remain unknown. In this study, a
region on the paternal sex ratio (PSR) chromosome was analyzed to investigate the mechanisms of tandem repeat evolution. The
region contains a junction between a tandem array of PSR2 repeats and a copy of the retrotransposon NATE, with other dispersed repeats (putative mobile elements) on the other side of the element. Little similarity was detected
between the sequence of PSR2 and the region of NATE flanking the array, indicating that the PSR2 repeat did not originate from the underlying NATE sequence. However, a short region of sequence similarity (11/15 bp) and an inverted region of sequence identity (8 bp) are
present on either side of the junction. These short sequences may have facilitated nonhomologous recombination between NATE and PSR2, resulting in the formation of the junction. Adjacent to the junction, the three most terminal repeats in the PSR2
array exhibited a higher sequence divergence relative to internal repeats, which is consistent with a theoretical prediction
of the unequal exchange model for tandem repeat evolution. Other NATE insertion sites were characterized which show proximity to both tandem repeats and complex DNAs containing additional dispersed
repeats. An ``accretion model' is proposed to account for this association by the accumulation of mobile elements at the
ends of tandem arrays and into ``islands' within arrays. Mobile elements inserting into arrays will tend to migrate into
islands and to array ends, due to the turnover in the number of intervening repeats.
Received: 18 August 1997 / Accepted: 18 September 1998 相似文献
20.
Microsatellite length variation was investigated at a highly variable microsatellite locus in four species of Apodemus. Information obtained from microsatellite allele sequences was contrasted with allele sizes, which included 18 electromorphs.
Additional analysis of a 400-bp unique sequence in the flanking region identified 26 different haplotype sequences or ``true'
alleles in the sample. Three molecular mechanisms, namely, (1) addition/deletion of repeats, (2) substitutions and indels
in the flanking region, and (3) mutations interrupting the repeat, contributed to the generation of allelic variation. Size
homoplasy can be inferred for alleles within populations, from different populations of the same species, and from different
species. We propose that microsatellite flanking sequences may be informative markers for investigating mutation processes
in microsatellite repeats as well as phylogenetic relationships among alleles, populations, and species.
Received: 3 November 1999 / Accepted: 2 May 2000 相似文献