PubMed · 9239511
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V Allamand, J S Beckmann. Mapping using linkage disequilibrium estimates: a comparative study.. https://doi.org/10.1159/000154418
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Hippophae rhamnoides ssp. turkestanica, a subdioecious plant inhabiting the cold desert of the Indian Himalaya, has gained immense recognition for its nutritional and medicinal values. In recent years, the plant species has proven to be a suitable system to understand the evolution of dioecy. Despite its biological significance, the cytogenetics of this dioecious plant is unclear due to various conflicting accounts of its X-Y chromosome system, particularly the length of Y-chromosome. In this study, we resolved these ambiguities through comprehensive cytogenetic analyses across diverse western Himalayan populations. Using morphometric analysis and fluorescence in situ hybridization (FISH) with a gender-specific marker (HRMSSR), we confirmed homomorphic XX chromosomes in females and heteromorphic sex-chromosomes in males with a notably smaller Y-chromosome. The investigation also revealed a predominant somatic chromosome number of 2n = 24, although minor deviations (2n = 18, 20, 22) appeared at the seed level. These findings highlight an evolutionarily advanced sex-chromosome system. This first detailed cytogenetic investigation of Himalayan Seabuckthorn provides critical insights into the chromosomal architecture, laying a crucial foundation for future evolutionary, genomic, and conservation studies in the species.
Loss of heterozygosity on chromosome 22q was detected in 53% of 123 ovarian carcinomas, suggesting the presence of at least one tumour suppressor gene. We have refined the location of one possible tumour suppressor gene to the region between the microsatellite markers D22S299 and CYP2D. Located within this region are the genes SREBP2 (sterol regulatory element binding protein 2) and NAGA (N-acetyl-alpha-D-galactosaminidase). Investigation of the coding exons of these genes by single stranded conformational polymorphism/heteroduplex analysis failed to identify any somatic genetic alterations in 57 ovarian tumours which exhibited LOH on 22q13. The CYP2D gene locus straddles the distal boundary of the candidate region. Germline variants of the active CYP2D6 gene with differing abilities to metabolise specific substrates have been implicated in the development of various cancers. Comparison of the frequency of the two common germline mutations among 258 ovarian tumours and 231 non-cancer controls did not reveal any significant differences between the two groups. This suggests that the known polymorphic variants of CYP2D6 are not involved in ovarian cancer predisposition. We also conclude that neither NAGA nor SREBP2 are likely to be mutated in ovarian carcinomas.
An autosomal recessive nonsyndromic deafness locus, DFNB10, was previously localized to a 12-cM region near the telomere of chromosome 21 (21q22.3). This locus was discovered in a large, consanguineous Palestinian family. We have identified and ordered a total of 50 polymorphic microsatellite markers in 21q22.3, comprising 16 published and 34 new markers, precisely mapped and ordered on BAC/cosmid contigs. Using these microsatellite markers, the locus for DFNB10 has been refined to an area of less than 1 Mb between markers 1016E7.CA60 and 1151C12.GT45. Six previously published cDNAs were mapped to this critical region, and their genomic structures were determined to facilitate mutation analysis in DFNB10. All six genes in this region (in order from centromere to telomere: White/ABCG1, TFF3, TFF2, TFF1, PDE9A, and NDUVF3) have been screened and eliminated as candidates for DFNB10. The new microsatellite markers and single nucleotide polymorphisms identified in this study should enable the refined mapping of other genetic diseases that map to 21q22.3. In addition, the critical region for DFNB10 has been reduced to a size amenable to an intensive positional cloning effort.