A genetic marker is a DNA sequence with a known physical location on a chromosome
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Peer-reviewed literature and reference texts discuss genetic markers and sequence-tagged sites in terms of their chromosomal locations and physical mapping.
Type 1 diabetes in the nonobese diabetic (NOD) mouse arises as a consequence of T cell-mediated destruction of the insulin-producing beta cells of the pancreas. Although little is known of the events that initiate and subsequently drive beta-cell destruction it is clear that the entire process is under complex genetic control. At present 19 loci have been mapped that influence the development of diabetes either at the level of initiation of insulitis or at the level of progression from insulitis to overt diabetes, or both. Previously, we have mapped one of these loci, Idd3, to a 0.35-cM interval on proximal mouse chromosome 3. In the present study we have narrowed the map position of this locus to an interval of 0.15 cM by a combination of novel congenic strains and an ancestral haplotype analysis approach. We have constructed a physical contig in bacterial artificial chromosome (BAC) clones across the minimal interval. Restriction mapping of the BAC contig placed the maximum size of the Idd3 interval at 780 kb between the markers D3Nds36 and D3Nds76. To refine further the Idd3 interval we developed a series of novel single nucleotide polymorphisms (SNPs) and carried out haplotype analysis on DNA from mouse strains known to carry either Idd3 susceptibility or protective alleles. This haplotype analysis identified a 145-kb segment of ancestral DNA between the microsatellite marker D3Nds6 and the SNP 81.3. One haplotype of this ancestral segment of DNA is found in mouse strains carrying an Idd3 susceptibility allele and another is found in mouse strains carrying an Idd3 protective allelle. Within the 780-kb congenically defined interval this 145-kb segment represents the most likely location for Idd3. The Il2 gene, which encodes the cytokine interleukin 2 (IL2), maps to this interval and is a strong candidate for Idd3. To investigate whether sequence variation exists in the promoter region of the Il2 gene, which might alter its expression, we sequenced the promoter region of the Il2 gene from mouse strains carrying either an Idd3 susceptibility or resistance allele. Two sequence variants were identified, neither of which fell in known regulatory elements within the Il2 promoter. In agreement with this observation steady-state Il2 mRNA levels showed no variation between susceptible and resistant mouse strains. These data suggest that the profound protection from diabetes seen in congenic mice carrying an Idd3 protective allele is unlikely to be due to differences in the level of expression of the Il2 gene. Instead, all of the current data support our hypothesis that Idd3 corresponds to amino acid variation at the amino terminus of Il2.
Radiation hybrid mapping uses radiation, such as x-rays, to break the DNA into fragments. The amount of radiation can be adjusted to create smaller or larger fragments. This technique overcomes the limitation of genetic mapping and is not affected by increased or decreased recombination frequency. Sequence mapping resulted from DNA sequencing technology that allowed for the creation of detailed physical maps with distances measured in terms of the number of base pairs. The creation of genomic libraries and complementary DNA (cDNA) libraries (collections of cloned sequences or all DNA from a genome) has sped up the process of physical mapping. A genetic site used to generate a physical map with sequencing technology (a sequence-tagged site, or STS) is a unique sequence in the genome with a known exact chromosomal location. An expressed sequence tag (EST) and a single sequence length polymorphism (SSLP) are common STSs. An EST is a short STS that is identified with cDNA libraries, while SSLPs are obtained from known genetic markers and provide a link between genetic maps and physical maps. Genetic maps provide the outline and physical maps provide the details.
Isolation of a novel mildly repetitive DNA sequence that is predominantly located at the terminus of the short arm of chromosome 4 near the Huntington disease gene.
A novel mildly repetitive DNA sequence that is reiterated approximately 20 times in the human genome has been isolated and characterized. Most of the repeat units are localized very near the terminus of the short arm of chromosome 4 (4p) in the region known to contain the Huntington disease (HD) gene. A cloned probe that detects the repeated sequence reveals a restriction fragment length polymorphism that is close to and/or distal to the most distal genetic locus on 4p. This probe, therefore, provides a new genetic marker very close to and possibly flanking the HD gene. In addition, this probe should prove very useful for detailed physical mapping of the most distal region of 4p around the HD gene. The few (two or three) copies of this repeat not located near the terminus of 4p are located near the ends of two other chromosomes, 14 and 21.
Published in Genomics (1989)
This technique overcomes the limitation of genetic mapping, and we can adjust the radiation so that increased or decreased recombination frequency does not affect it. Sequence mapping resulted from DNA sequencing technology that allowed for creating detailed physical maps with distances measured in terms of the number of base pairs. Creating genomic libraries and complementary DNA (cDNA) libraries (collections of cloned sequences or all DNA from a genome) has sped the physical mapping process. A genetic site that scientists use to generate a physical map with sequencing technology (a sequence-tagged site, or STS) is a unique sequence in the genome with a known exact chromosomal location. An expressed sequence tag (EST) and a single sequence length polymorphism (SSLP) are common STSs. An EST is a short STS that we can identify with cDNA libraries, while we obtain SSLPs from known genetic markers, which provide a link between genetic and physical maps. Genetic maps provide the outline and physical maps provide the details. It is easy to understand why both genome mapping technique types are important to show the big picture.
Identification and regional localization of DNA markers on chromosome 7 for the cloning of the cystic fibrosis gene.
To facilitate mapping of the cystic fibrosis locus (CF) and to isolate the corresponding gene, we have screened a flow-sorted chromosome 7-specific library for additional DNA markers in the 7q31-q32 region. Unique ("single-copy") DNA segments were selected from the library and used in hybridization analysis with a panel of somatic cell hybrids containing various portions of human chromosome 7 and patient cell lines with deletion of this chromosome. A total of 258 chromosome 7-specific single-copy DNA segments were identified, and most of them localized to subregions. Fifty three of these corresponded to DNA sequences in the 7q31-q32 region. Family and physical mapping studies showed that two of the DNA markers, D7S122 and D7S340, are in close linkage with CF. The data also showed that D7S122 and D7S340 map between MET and D7S8, the two genetic markers known to be on opposite sides of CF. The study thus reaffirms the general strategy in approaching a disease locus on the basis of chromosome location.
Published in American journal of human genetics (1988)
Arbetets uppgift var att identifiera en DNA-sekvens som skulle kunna finnas hos storspiggens könsbestämningsregion. Avsikten med detta arbete är att utveckla en enkel PCR-baserad metod för att kunna könsbestämma storspiggar genetiskt. Tidigare genetiska studier har visat en skillnad mellan honor och hanar vid jämförelse av deras RAPD-3 PCR produkter. Skillnaden består i att endast hanarna har ett fragment som är runt 250 bp stort. Detta fragment ska isoleras, renas, klonas och sekvenseras med hjälp av olika metoder. Sekvensen ska användas för att beställa designerade primer som testades för at
Three genera of pocket gophers occur in Texas: Cratogeomys in the western third of the state, Thomomys in the montane regions of the Trans-Pecos Region and the southwestern portion of the Edwards Plateau, and Geomys statewide except for portions of the Trans-Pecos Region. However, due to considerable morphological conservation, differentiating among species and subspecies has been difficult, if not impossible. Advanced molecular markers such as DNA sequencing have proven useful in defining species boundaries and in generating phylogenetic relationships at the species level, but general taxon s
Systematic review and meta-analysis of the genetic associations of primary angle-closure disease (PACD). To confirm the genetic biomarkers for PACD, including primary angle-closure glaucoma (PACG) and related phenotypes. We searched in the MEDLINE and EMBASE databases for genetic studies of PACG or other PACD published from the start dates of the databases to May 11, 2015. We estimated the summary odds ratios (ORs) and 95% confidence intervals (CIs) for each polymorphism in PACG, primary angle-closure suspect (PACS), and primary angle-closure (PAC) using fixed- or random-effect models. We also performed sensitivity analysis to test the robustness of the results. Our literature search yielded 6463 reports. Among them, we identified 24 studies that fulfilled the eligibility criteria for meta-analysis, involving 28 polymorphisms in 11 genes/loci. We affirmed the association of PACG and combined PACS/PAC/PACG with 10 polymorphisms in 8 genes/loci, including COL11A1 (rs3753841-G, OR, 1.22; P = 0.00046), HGF (rs17427817-C, OR, 2.02; P = 6.9E-07; rs5745718-A, OR, 2.11; P = 9.9E-07), HSP70 (rs1043618, GG+GC, OR, 0.52; P = 0.0010), MFRP (rs2510143-C, OR, 0.66; P = 0.012; rs3814762-G, OR, 1.40; P = 0.0090), MMP9 (rs3918249-C, OR, 1.35; P = 0.034), NOS3 (rs7830-A, OR, 0.80; P = 0.036), PLEKHA7 (rs11024102-G, OR, 1.24; P = 8.3E-05), and PCMTD1-ST18 (rs1015213-A, OR, 1.59; P = 0.00013). Sensitivity analysis indicated that the results were robust. In this study, we confirmed multiple polymorphisms in 8 genes/loci as genetic biomarkers for PACD, among which 3 were identified in a genome-wide association study (COL11A1, PLEKHA7, and PCMTD1-ST18), and 5 were identified in candidate gene studies (HGF, HSP70, MFRP, MMP9, and NOS3).
Allergic rhinitis (AR) is a type I hypersensitivity disease of the nasal mucosa that is mediated by immunoglobulin E (IgE). The relationship between the rs2569190 polymorphism of the CD14 gene and the risk of AR remains unclear. Therefore, we performed a meta-analysis to evaluate this relationship. We performed a systematic search and found 8 relevant publications that were included in this meta-analysis, consisting of 1,022 cases and 1,045 controls. Statistical analyses were conducted via the "meta" package in R studio. The odds ratios (ORs) with corresponding 95% confidence intervals (CIs) were calculated. No association was found between CD14 rs2569190 and AR risk in the total study population. However, subgroup analysis revealed that the rs2569190 T allele was most likely associated with an increased risk of AR in the Egyptian subgroup [allelic model (T vs. C): OR = 2.56, 95% CI = 1.49-4.43, I<sup>2</sup> = 60.8%; homozygous model (TT vs. CC): OR = 12.50, 95% CI = 1.50-103.95, I<sup>2</sup> = 77.1%; recessive model (TT vs. CT + CC): OR = 4.55, 95% CI = 2.46-8.41, I<sup>2</sup> = 0]. On the other hand, rs2569190 was not significantly associated with AR risk in other populations. In summary, our meta-analysis revealed that rs2569190 has potential as a candidate marker of AR for further investigation in the Egyptian population. However, owing to the limitations of this study, our findings are insufficient to support immediate clinical applications. Further high-quality studies with larger sample sizes are needed.
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