Karyotaxonomische Untersuchungen anPotentilla taurica s.l. in Bulgarie

Several taxa considered by previous authors as intraspecific ofPotentilla taurica s.l. are considered as separate species. A diploid chromosome number 2n=14 and the characteristic chromosomes of karyotypes of 3 Balkan endemicsP. ni?i?i Adam.,P. emilipopii Nyarády andP. pirotensis (Borb.) Mark. are recorded.P. bornmuelleri Borb.,P. mollicrinis (Borb.) Stankov andP. astracanica Jacq. are widespread in South-eastern Europe. Of this groupP. mollicrinis is a diploid (2n=14),P. bornmuelleri is tetraploid and inP. astracanica a polyploid serie of 2x=14, 4x=28, 5x=35 and 6x=42 has been found. The karyotypes of all species are characterized by submetacentric chromosomes.     

Intraspecific nuclear DNA variation in Drosophila

We have summarized and analyzed all available nuclear DNA sequence polymorphism studies for three species of Drosophila, D. melanogaster (24 loci), D. simulans (12 loci), and D. pseudoobscura (5 loci). Our major findings are: (1) The average nucleotide heterozygosity ranges from about 0.4% to 2% depending upon species and function of the region, i.e., coding or noncoding. (2) Compared to D. simulans and D. pseudoobscura (which are about equally variable), D. melanogaster displays a low degree of DNA polymorphism. (3) Noncoding introns and 3' and 5' flanking DNA shows less polymorphism than silent sites within coding DNA. (4) X-linked genes are less variable than autosomal genes. (5) Transition (Ts) and transversion (Tv) polymorphisms are about equally frequent in non-coding DNA and at fourfold degenerate sites in coding DNA while Ts polymorphisms outnumber Tv polymorphisms by about 2:1 in total coding DNA. The increased Ts polymorphism in coding regions is likely due to the structure of the genetic code: silent changes are more often Ts's than are replacement substitutions. (6) The proportion of replacement polymorphisms is significantly higher in D. melanogaster than in D. simulans. (7) The level of variation in coding DNA and the adjacent noncoding DNA is significantly correlated indicating regional effects, most notably recombination. (8) Surprisingly, the level of polymorphism at silent coding sites in D. melanogaster is positively correlated with degree of codon usage bias. (9) Three proposed tests of the neutral theory of DNA polymorphisms have been performed on the data: Tajima's test, the HKA test, and the McDonald-Kreitman test. About half of the loci fail to conform to the expectations of neutral theory by one of the tests. We conclude that many variables are affecting levels of DNA polymorphism in Drosophila, from properties of nucleotides to population history and, perhaps, mating structure. No simple, all encompassing explanation satisfactorily accounts for the data.      

A molecular phylogeny for the Drosophila melanogaster subgroup and the problem of polymorphism data

Drosophila melanogaster belongs to a closely related group of eight species collectively known as the melanogaster subgroup; all are native to sub-Saharan Africa and islands off the east coast of Africa. The phylogenetic relationships of most species in this subgroup have been well documented; however, the three most closely related species, D. simulans, D. sechellia, and D. mauritiana, have remained problematic from a phylogenetic standpoint as no data set has unambiguously resolved them. We present new DNA sequence data on the nullo and Serendipity-alpha genes and combine them with all available nuclear DNA sequence data; the total data encompass 12 genes and the ITS of rDNA. A methodological problem arose because nine of the genes had information on intraspecific polymorphisms in at least one species. We explored the effect of inclusion/exclusion of polymorphic sites and found that it had very little effect on phylogenetic inferences, due largely to the fact that 82% of polymorphisms are autapomorphies (unique to one species). We have also reanalyzed our previous DNA-DNA hybridization data with a bootstrap procedure. The combined sequence data set and the DNA-DNA hybridization data strongly support the sister status of the two island species, D. sechellia and D. mauritiana. This at least partially resolves what had been a paradox of parallel evolution in these two species.      

Microcalorimetric studies on the lyophilic properties of pectic substances

The exothermic effects observed on wetting pectins with water and aliphatic alcohols were studied using a microcalorimeter.The heat released on wetting 1 g pectin with water was found to be 171 ± 7·5 J g^?1. It was experimentally established that 1 g of dry pectin exothermically bonded up to 0·57 g of water.By using the Gibbs-Helmholtz-Young equation which relates the heat released by wetting to the area of the wetted surface, it was estimated that the surface accessible to water in 1 g of pectin was 1·46 × 10³ m² g^?1. The heat of hydration was independent of the degree of esterification of the pectin. The experimental results revealed that there were about six molecules of energetically bonded water per monomer unit of pectin.A specific interaction between methanol and the methoxyl groups of pectin was observed on wetting pectins with methanol and dependence was established between the released heat and the degree of esterification. No similar dependence was reported for the remaining aliphatic alcohols.     

Sensitivity of sea urchin early embryos to antagonists of acetylcholine and monoamines

Early embryos of A. lixula are 10–800 times more sensitive to several neuropharmaca than are early embryos of 6 other studied species of sea urchins. Of 53 neuropharmaca studied, 25 were found hyperactive; of 19 other inhibitors of development (mitotic and metabolic poisons) only antimycin A was hyperactive for A. lixula. Both hyperactive neuropharmaca and neuropharmaca with normal activity suppress cleavage divisions and inhibit protein biosynthesis acting as antagonists of intracellular acetylcholine and monoamines. The mechanism responsible for the normal sensitivity and hypersensitivity of early sea urchin embryos is discussed.     

Repetitive sequences in nuclear deoxyribonucleic acid ofSaccharomyces cerevisiae

Nuclear DNA isolated from aSaccharomyces cerevisiae ρ mutant was studied for the presence of repetitive sequences. A main-band DNA preparation free of rRNA genes and 2-μm plasmid DNA was prepared by density gradient centrifugation in Cs₂SO₄−Ag⁺. A fast renaturing fraction was obtained from this mainband DNA by 3 cycles of reassociation at a low C₀t value (0.2). This fraction reassociated 10 times faster than the bulk of the main-band DNA. Its sequences comprised about 3% of the genome and showed a considerable heterogeneity in respect to repetitiveness. The relationship of this fraction to the repetitive transposable elements recently found in yeast cells is discussed.