A possible cause of non-disjunction of additional chromosome 21 in Down syndrome

Summary A possible cause of non-disjunction of chromosome 21 in Down Syndromes has been cytogenetically evaluated by examining the parents by Ag-staining technique. In all the cases studied so far, the contributing parents have active ribosomal cistrons on both chromosomes 21 i.e. both chromosomes are stained positively by silver staining. These results show that the active NORs might play an essential role in meiotic non-disjunction. Furthermore, the preliminary results demonstrate that the acrocentric associations of homologous and non-homologous nature involving chromosome 21 are the most frequent in the contributing parent which may further indicate the role of multiple cellular factors affecting the associations in promoting the non-disjunction in addition to active NORs. The possible mechanisms regarding the non-disjunction of chromosome 21 have been described.Presented at the 34th Annual Meeting of the American Society of Human Genetics, Norfolk, VA, USA     

The impact of a salinity barrier on the partitioning of heavy metals in sediments of a tropical backwater system

Abstract

Concentrations of heavy metals (Cd, Co, Cr, Cu and Fe) in surface sediments and their partitioning behaviour between exchangeable, reducible (Fe-Mn oxide bound) and organic/residual phases of the sediments in a typical backwater system of Kerala, viz. the southern upstream part of Cochin Estuarine System (South India), have been studied. Spatial and temporal variations of trace metals are discussed with special reference to pH, dissolved oxygen, salinity, organic carbon and texture of sediment. Metal concentrations in the tide gated part of the estuary were found to be significantly higher when compared to metal concentrations reported from the unrestricted part of the Cochin estuarine system and also those from many of the unpolluted estuaries worldwide. The higher levels of heavy metals in the study area and their characteristic distribution and partitioning behaviour in the surficial sediments were attributed to the presence of a salinity barrier across the backwater system and also by the massive use of pesticides and chemical fertilizers in the vast area of agricultural land near the backwater system.     

The Genetic Structure and Evolutionary Fate of Parthenogenetic Amphibian Populations as Determined by Markovian Analysis

SYNOPSIS. One-locus, two-allele models are presented which describethe genetic consequences of naturally occurring andexperimentallyinduced parthenogesis in triploid and diploid amphibians. Themodels may in general be used to investigate genetic changeresulting from apomictic (ameiotic) and automictic (meiotic)parthenogenetic reproduction. These models quantify the influence of mutation, segregation,and selection upon genetic variability in parthenogeneticpopulations.They also allow an estimate of the relative importance of stochasticforces in altering this variability. They thus provide a basisfor understanding evolution in these populations. Some of the conclusions derived from this study contradict previouspredictions regarding genetic variability in parthenogeneticpopulations. First, if mutation is the sole source of geneticchange (i.e., strict apomixis), parthenogenetic populationsshould not become completely heterozygous. Second, small amountsof segregation occurring in apomictic populations have enormouseffects upon the genetic variability of these populations, i.e.,they should lose much of their heterozygosity. In addition to these conclusions, the results of this studysuggest that studies of protein variability in parthenogeneticspecies should contribute toward answering the question: Howmuch of the genetic variability observed in nature is evolutionarilyrelevant?     

Dating of graptolite zones by sedimentation rates: implications for rates of evolution

Preliminary determinations of ancient pelagic sedimentation rates agree with modern rates at about 4 meters per million years. By combining data on the thickness of graptolite zones from the North American Cordillera with data from other parts of the world, we have refined the Early Silurian time scale and obtained much better resolution than is possible for radiometric dates. The new Early Silurian time scale allows estimation of true rates of change in graptolite diversity. The Llandoverian diversity explosion is twice as rapid as was previously thought. The brevity of diversity lows and rapidity of speciation support modern theories of quantum evolution.     

Assessment of genetic diversity and population structure in pomegranate (Punica granatum L.) using hypervariable SSR markers

Physiology and Molecular Biology of Plants - The present study investigates the genetic diversity and population structure among 42 diverse pomegranate genotypes using a set of twenty one class I...     

Comparative analysis of metabolites in contrasting chickpea cultivars

Journal of Plant Biochemistry and Biotechnology - Chickpea (Cicer arietinum L.) is a good source of nutrients for animals and human consumption. In the present study, we analyzed the anthocyanin...     

TP53 codon 72 polymorphism and type 2 diabetes: a case–control study in South Indian population

Molecular Biology Reports - TP53 functions primarily as a tumor suppressor, controlling a myriad of signalling pathways that prevent a cell from undergoing malignant transformation. This tumor...