PubMed · 4992702
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1971-01-16. Chromosome mapping.. https://pubmed.ncbi.nlm.nih.gov/4992702/
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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.
Pseudohypoparathyroidism type Ib (PHP-Ib) is a paternally imprinted disorder which maps to a region on chromosome 20q13.3 that comprises GNAS1 at its telomeric boundary. Exon A/B of this gene was recently shown to display a loss of methylation in several PHP-Ib patients. In nine unrelated PHP-Ib kindreds, in whom haplotype analysis and mode of inheritance provided no evidence against linkage to this chromosomal region, we confirmed lack of exon A/B methylation for affected individuals, while unaffected carriers showed no epigenetic abnormality at this locus. However, affected individuals in one kindred (Y2) displayed additional methylation defects involving exons NESP55, AS and XL, and unaffected carriers in this family showed an abnormal methylation at exon NESP55, but not at other exons. Taken together, current evidence thus suggests that distinct mutations within or close to GNAS1 can lead to PHP-Ib and the associated epigenetic changes. To further delineate the telomeric boundary of the PHP-Ib locus, the previously reported kindred F, in which patient F-V/51 is recombinant within GNAS1, was investigated with several new markers and direct nucleotide sequence analysis. These studies revealed that F-V/51 remains recombinant at a single nucleotide polymorphism (SNP) located 1.2 kb upstream of XL. No heterozygous mutation was identified between exon XL and an SNP approximately 8 kb upstream of NESP55, where this affected individual becomes linked, suggesting that the genetic defect responsible for parathyroid hormone resistance in kindred F, and probably other PHP-Ib patients, is located >or=56 kb centromeric of the abnormally methylated exon A/B. A region upstream of the known coding exons of GNAS1 is therefore predicted to exert, presumably through imprinting of exon A/B, long-range effects on G(s)alpha expression.
The rapid development of a dense single-nucleotide-polymorphism marker map has stimulated numerous studies attempting to characterize the magnitude and distribution of background linkage disequilibrium (LD) within and between human populations. Although genotyping errors are an inherent problem in all LD studies, there have been few systematic investigations documenting their consequences on estimates of background LD. Therefore, we derived simple deterministic formulas to investigate the effect that genotyping errors have on four commonly used LD measures-D', r, Q, and d-in studies of background LD. We have found that genotyping error rates as small as 3% can have serious affects on these LD measures, depending on the allele frequencies and the assumed error model. Furthermore, we compared the robustness of D', r, Q, and d, in the presence of genotyping errors. In general, Q and d are more robust than D' and r, although exceptions do exist. Finally, through stochastic simulations, we illustrate how genotyping errors can lead to erroneous inferences when measures of LD between two samples are compared.