Browsing by Subject "microsatellites"
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Item Development of Microsatellite Markers for Loxosceles devia Gertsch & Mulaik (Araneae: Sicariidae) using Next Generation SequencingGarza, Tanya Y; Mott, DanBrown recluse spiders in the genus Loxosceles are known for causing severe necrotic skin lesions. Despite their impact on human health, very little is known concerning the genetic diversity or population structure of this genus. The development of a suite of molecular markers (microsatellites) would allow us to obtain genetic data and expand the resources available to study Loxosceles devia, the species found throughout south Texas. Microsatellites are long tandem repeats about 1-6 nucleotides long of DNA, also known as simple sequence repeats. Their co-dominant method of inheritance, wide spread distribution across the nuclear genome, ease of scoring, and high mutation rates make microsatellites an ideal molecular marker. Unfortunately, the cost of developing microsatellites has limited their availability until now. The Ion Torrent Personal Genome Machine® was used to shotgun sequence libraries of genomic DNA derived from L. devia. The program MSATCOMMANDER™ was used to identify and design primers for di-, tri-, and tetra- microsatellite repeats from these shotgun sequences. Seventeen microsatellite markers were designed and polymerase chain reaction conditions were optimized for each primer to develop a suite of novel molecular markers for this species.Item Evolutionary implications of microsatellite variation in the Peromyscus maniculatus species group(Texas A&M University, 2004-11-15) Chirhart, Scott EdwardGiven the distribution and probable evolutionary history of the Peromyscus maniculatus species group, an interspecific comparison of microsatellite variation among these species would be logically based (at least initially) on primers isolated from the genome of a geographically central population of P. maniculatus. Additionally, as the species in the group are recently diverged, reasonably informative microsatellite data are likely to require analysis of a rapid evolving category of microsatellite loci. The initial phase of this research involved the isolation, characterization and assessment of variation for a panel of DNA microsatellites containing perfect dinucleotide repeats from a geographically central population of P. maniculatus. Theoretical predictions and empirical studies indicate that phylogenetic analyses based on microsatellite primers isolated from a focal species may be subject to ascertainment biases that can be expected to degrade the efficacy of this approach with increasing phylogenetic depth between the species from which the microsatellites were isolated and those to which these loci are being compared. Results of an analysis of allelic variation at 12 pure, dinucleotide microsatellite loci (isolated from P. maniculatus) are reported for samples of all species in the P. maniculatus species group and the sister taxon P. leucopus. Examined for the species in the P. maniculatus species group for which there is an a priori highly corroborated phylogeny, evidence of ascertainment bias was apparent only for one locus that was unique to P. maniculatus. Genealogical analyses of the data over all loci yielded inferred relationships that were entirely concordant with the a priori corroborated phylogeny for P. maniculatus, P. keeni, P. polionotus, P. melanotis and P. leucopus. Genealogical analyses of the previously unresolved relationships of P. keeni and P. sejugis consistently placed these as an independent sister-group between P. maniculatus and P. polionotus. The geographically improbable sister-group association of P. keeni and P. sejugis may be the result of an historical ancestral continuity or may reflect large-scale lineage sorting rather than true phylogenetic propinquity. These data suggest that, given the choice of an appropriate focal species, even relatively small sets of pure dinucleotide microsatellites can provide reliable population genetic and systematic implications for taxa with divergence times dating to the Pleistocene.Item Genetic analysis of the endangered silver rice rat (Oryzomys palustris natator) and Lower Keys marsh rabbit (Sylvilagus palustris hefneri)(Texas A&M University, 2007-04-25) Crouse, Amanda LouiseGenetic analyses of two endangered species of mammals in the Lower Keys of Florida (Lower Keys marsh rabbit, LKMR, Sylvilagus palustris hefneri; silver rice rat, SRR, Oryzomys palustris natator) were performed to evaluate the genetic structure of their populations. Mitochondrial sequence data (control region; 763 base pairs (bp), LKMR; 788 bp, SRR) were used to explore patterns of genetic variation within and among island populations in both species. Analysis of the SRR also included 8 polymorphic nuclear microsatellite loci (9 to 16 alleles). Phylogenetic analyses of mitochondrial sequence data for both species revealed two main lineages corresponding to eastern and western localities, with high levels of genetic structuring (LKMR FST = 0.982, SRR ????ST = 0.916). The two species differed in the level of sequence divergence between eastern and western populations (LKMR, 19 bp; SRR 4 bp). In addition to an overall similar pattern of genetic subdivision, populations of both species possessed low levels of mtDNA variation (haplotypic diversity in the LKMR = 66.1%, SRR = 58.6%). Microsatellite analyses of the SRR revealed subdivision between eastern and western regions. Although less pronounced than the structure observed in mtDNA, the overall pattern was still apparent. Additional examination of divergence between mainland and Lower Keys rice rats revealed a genetic division that indicated a lack of recent gene exchange between the regions (i.e. no shared haplotypes, the presence of private alleles, and distinctive separation in numerous analyses). Although this degree of division does not warrant species designation, the levels and patterns of divergence, both morphological and genetic, do suggest genetic isolation of mainland and island forms. This fact, along with restricted gene flow between the Lower Keys and the Everglades, suggests that the SRR is on an evolutionary trajectory separate from its mainland counterparts and validates its identification as a separate subspecies, Oryzomys palustris natator. Finally, the genetic division between eastern and western populations of the SRR and LKMR suggests that populations of both species in these two regions of the Lower Keys should be treated as separate management units, especially when considering the enhancement of populations via translocations.Item Genetic variation in Atlantic yellowfin tuna (Thunnus albacares) to assess stock structure and reproductive variance(Texas A&M University, 2005-02-17) Farnham, Tiffany TalleyThe population genetic structure of Atlantic yellowfin tuna (Thunnus albacares) has received little attention despite the substantial fishing mortality of juveniles caused by purse seining around fish aggregating devices in the Gulf of Guinea targeting multi-species schools that also include similarly sized skipjack tuna (Katsuwonus pelamis) and bigeye tuna (T. obesus). We used sequence data from 355 bp of the mitochondrial control region I as well as six microsatellite loci to examine: (1) population structure, and (2) to look for evidence of reproductive variance. We analyzed two samples of adults from the Gulf of Mexico (GOM) and one sample of early juveniles (20-50 mm) from the Gulf of Guinea (GOG). We found no evidence of geographic or temporal differentiation among the samples. Accordingly, the null hypothesis of panmixia for yellowfin tuna in the Atlantic Ocean could not be rejected. A sudden expansion analysis based on mtDNA control region I sequence data of yellowfin tuna was highly significant. Time estimates for expansion were between 40,000 and 80,000 years before present. The associated high levels of homoplasy could be masking any existing population structure. Additional sampling from additional locations and across several years will be needed to test the hypothesis of panmixia. We also provide preliminary evidence of the Allendorf-Phelps effect, which may contribute to reproductive variance. This is the first evidence of this effect in any other tuna or pelagic species. Data indicates that early juveniles sharing the same mtDNA control region I haplotype were caught in the same tow and had a significant probability of halfsibship status as calculated from their haplotype and genotype at one microsatellite locus through kinship analysis. Sampling throughout the spawning season and across several years, as well as analysis with additional microsatellite loci that have a more even distribution of alleles, will be needed to more fully identify the sibling status of larvae and early juveniles caught in the same tow as well as the extent of this reproductive variance.Item Genomic analysis of the horse Y chromosome(Texas A&M University, 2005-02-17) Santani, Avni BhawanStallion fertility is of significant economic importance in the multibillion dollar equine industry. Presently, the underlying genetic causes of infertility in stallions are unknown. Analysis of the human genome has shown that in more than 25% of cases, male infertility is associated with deletions/rearrangements in the Y chromosome. Presently there is no gene map for the Y chromosome in the horse. Therefore, the primary aim of this study is to build a detailed physical map of the chromosome with a long-term aim to identify and analyze Y-specific factors affecting fertility in stallions. To materialize this, we constructed the first radiation hybrid and FISH map of the euchromatic region of the horse Y chromosome. This basic map was used to obtain Y-specific BAC clones that provided new STS markers from the end sequences. Chromosome walking provided 73 BACs comprising 7 contigs that were built across the euchromatic region using 124 markers for content mapping. The results were validated by restriction fingerprinting and Fiber FISH. The map is presently the most informative among the domestic species and second to only human and mouse Y chromosome maps. The construction of this map will pave the way for isolation and functional characterization of genes critical for normal male fertility and reproduction and will in the future lead to the development of a diagnostic test to facilitate early identification of deletions/rearrangements on the Y chromosome of potentially affected foals/stallions. The second part of the study comprised the first extended investigation to assess genetic variation in the horse Y chromosome. Approximately 4.5Mb of the euchromatic region was screened for polymorphic microsatellite markers. Of the 27 markers that were characterized and screened for polymorphism in 14 breeds of the domestic horse and eight extant equids, only one was polymorphic in the domestic horse, suggesting a low level of genetic variation on the chromosome. However, 21 of the markers showed noteworthy variation (on average four alleles/marker) among the eight equids. These markers will be vital in future studies aimed at elucidating the genetic relationships between the various equids through phylogenetic analysis.Item Temporal genetic structure of feral honey bees (Hymenoptera: Apidae) in a coastal prairie habitat of southern Texas: impact of Africanization(Texas A&M University, 2004-09-30) Pinto, Maria AliceThe goal of this study was to examine the impact of Africanization on the genetic structure of the Welder Wildlife Refuge feral honey bee population by scoring mtDNA and microsatellite polymorphisms. Adult honey bee workers, collected between 1991 and 2001, were screened for mtDNA using the cytochrome b/BglII, ls rRNA/EcoRI, and COI/HinfI PCR-based assays. The procedure allowed identification of four mitotypes: eastern European, western European, A. m. lamarckii, and A. m. scutellata. The relative frequencies of the four mitotypes changed radically during the 11-year period. Prior to immigration of Africanized honey bees, the resident population was essentially of eastern European maternal ancestry. The first colony of A. m. scutellata mitotype was detected in 1993. Between 1995 and 1996 there was a mitotype turnover in the population from predominantly eastern European to predominantly A. m. scutellata. From 1997 onward, most colonies (69 %) were of A. m. scutellata mitotype. The temporal change in mtDNA was paralleled by nuclear DNA. The 12 microsatellite loci analyzed indicated (1) the mechanism of Africanization of the Welder population involved both maternal and paternal bi-directional gene flow (hybridization) between European and Africanized honey bees; and (2) the resident panmitic European population was replaced by panmitic asymmetrical admixtures of A. m. scutellata and European genes. The steepest increase in the proportion of introgressed A. m. scutellata nuclear alleles occurred between 1994 and 1997. The post-Africanization gene pool was composed of a diverse array of recombinant classes with a substantial European genetic contribution (mean proportion of European-derived alleles was 37 % as given by mR estimator or 25 % as given by mY estimator, for 1998-2001). If European genes continue to be retained at moderate frequencies, then the Africanized population is best viewed as a "hybrid swarm" instead of "pure African". The most radical change in the genetic structure of the Welder Wildlife Refuge feral honey bee population (observed between 1995 and 1997) coincided with arrival of the parasitic Varroa mite. We suggest that Varroa likely hastened the demise of European honey bees and had a major role in restructuring the Welder Wildlife Refuge feral honey bee population.