Biomedical subjects

R Chakraborty

Publications and source records attributed to R Chakraborty.

312 records · Page 18Linked to original sources

PubMedDate not supplied

Study of three hypervariable DNA loci (D1S7; D7S22 and D12S11) in three European populations.

To investigate the population genetic characteristics and genetic affinity, DNA profiles of three highly polymorphic VNTR (variable number of tandem repeats) loci (D1S7; D7S22 and D12S11) were studied in 405 individuals from three major European populations (English, Spanish and Basques). Like other studies on VNTRs, a large significant heterozygote deficiency was observed in all three populations. This decrease was ascribed to the limitation, coalescence and non-detectibility of alleles associated with the RFLP (restriction fragment length polymorphism) technique, through which the VNTR loci are genotyped. When the non-detectable alleles were taken into consideration, analyses of fragment sizes at these loci within each sample, as well as their fixed binned analyses, reveal that the assumptions of independence of allelelic occurrences within and between loci are valid for this European data. By comparing genetic variation at three VNTR loci with 17 blood groups, proteins and HLA loci in three well defined European populations, it is shown that the pattern of differentiation at these sets of loci are in general parallel especially for the hypervariable loci HLA and VNTR. Fixed-bin allele frequencies, therefore, are the best descriptions of such a database both for population genetic and forensic calculation studies. The Basques, with regard to VNTR loci, do not show any reduced genetic variability compared to other two European populations (English and Spanish).

Chromosome Mapping↗

PubMedDate not supplied

Statistical power of an exact test of Hardy-Weinberg proportions of genotypic data at a multiallelic locus.

A computer algorithm for numerical evaluation of the statistical power of an exact test of Hardy-Weinberg genotypic proportions (HWP), developed here, indicates that the power is dependent on the number of segregating alleles as well as allele frequencies. While low levels of departure from the null hypothesis are difficult to detect from single-locus data, should such deviation be due to population substructuring, multiple loci, at each of which the number of segregating alleles is large (as seen with hypervariable loci), may easily detect even low levels of departure from HWP. Undetected small levels of departure may still provide conservative estimates of genotype frequencies from allele frequency data, following the current practice in forensic genetics.

Algorithms↗

PubMedDate not supplied

Estimating the frequency of nonpaternity in Switzerland.

In linkage analysis and gene mapping in general, typing error and/or errors in specifying pedigree relationships between individuals typically lead to an upwards bias in recombination fraction estimates and to a loss of power for detecting linkage. [Ott J: Analysis of Human Genetic Linkage. Baltimore, Johns Hopkins University Press, 1991]. The presence of nonpaternity is the most common source of error of misspecification of pedigree relationships between individuals that can have a negative impact on pedigree analysis. We have developed estimates of underlying nonpaternity probabilities based on observed Mendelian inconsistencies. The methods were applied to a sample of 1,607 children and their parents. Genetic marker data were investigated to test for exclusions due to nonpaternity. Among the 1,607 children, 11 or 0.68% exclusions were found. When a constant nonpaternity rate was assumed for each child, its maximum likelihood estimate turned out to be 0.78% with asymptotic 95% confidence limits of 0.41% and 1.35%. When varying nonpaternity rates were assumed, its mean was estimated as 0.83% with asymptotic 95% confidence limits of 0.32% and 1.33%.

Child↗

PubMedDate not supplied

A test of allelic independence based on distributions of allele size differences at microsatellite loci.

Thousands of polymorphic microsatellite loci are now mapped in the human genome, most of which exhibit a large number of segregating alleles. For forensic, evolutionary and gene mapping applications, it is important to establish intralocus allelic independence at these loci. We develop a test for intralocus allelic independence based on repeat size differences between alleles within genotypes of individuals, and show its relationship with the intraclass correlation of allele sizes within loci. Applications of this test to 13 short tandem repeat loci in 4 subpopulations indicate that the distribution of size differences of alleles has adequate power to detect intralocus dependence of alleles caused by population substructure. In addition, size differences between randomly chosen alleles provide information regarding heterozygosity and contiguity of allele sizes at the locus, which by themselves do not necessarily indicate the presence of population substructure.

Alleles↗

PubMedDate not supplied

Is being Hispanic a risk factor for non-insulin dependent diabetes mellitus (NIDDM)?

The objective of this paper is to critically assess the basis of the hypothesis that the ethnicity of Hispanics is by itself a risk factor of NIDDM. Showing that the definition of the term Hispanics has both operational and methodological problems, it is argued that in the United States, a group identified by this term is genetically, as well as culturally, heterogeneous. Further, the actual risk factors of NIDDM may simply co-vary with the ethnicity of Hispanics, so that the notion that this ethnicity is a stand-alone independent risk factor of NIDDM may be too simplistic.

Diabetes Mellitus, Type 2↗

PubMedDate not supplied

Complex segregation analysis of facial clefting in Chile.

Nonsyndromic cleft lip with or without cleft palate (CL/P) has an incidence of 1.5 per 1,000 live births in Chile, with 1.7 per 1,000 in males and 1.3 per 1,000 in females, which is nearly the same as the level found in Asian populations. The high rate of occurrence of CL/P in Chile is probably due to the presence of Amerindian genes in Chilean populations. Using the computer program PAP, a complex segregation analysis of CL/P was conducted for 67 multigeneration pedigrees from Chile, each ascertained from one affected proband. These pedigrees yielded 162 affected individuals and over 898 family members who were included in the analysis. The most parsimonious model of transmission indicated the presence of an autosomal dominant gene with reduced (20-25%) penetrance.

Chile↗