Studies on bacterial conjugational crosses via model populations. I. The model populations

A procedure is presented in which model populations, simulating progenies obtained from Escherichia coli Hfr x F- crosses, are generated. The procedure seems to be appropriate for visualizing hidden features of the genetic analysis, which are not detected by the conjugational crosses.     

Studies on bacterial conjugational crosses via model populations. III. Reproduction of results of Hfr x F- crosses in Escherichia coli

Hfr x F- recombinational genome interactions are simulated by a computer program. Genotype spectrums of selected samples from Hfr x F- crosses of Escherichia coli, found in the published literature, are reproduced. Relevance of the findings for interpretation of conjugational results in Escherichia coli is discussed.     

Genetic studies on some Nepalese populations

Populations living in two different regions of Nepal have been studied. The first region (the Kali Gandaki valley) is inhabited mainly by Magars, Gurungs, Thakalis and Chetris. It has been found that they exhibit different ABO gene frequencies though living in very close areas and often in the same villages. Thus they are still genetically different entities besides being ethnically distinguishable from each other.The second region examined in the present survey (the Solu Khumbu) is inhabited by Sherpas. They were studied for markers not analysed in a previous research, namely for ABO, UMPK, PGD, GLO and LDH.     

Genetic studies in dioeciousmelandrium. II

The process of sex determination leads to the formation of the sex organs. Formerly two different groups of sex-determining genes were distinguished: the sex-promoting genes causing the actual development of the sex organs, and sex-deciding genes, which decide whether female-promoting genes, or male-promoting genes, or both come into action, thus giving rise to female flowers, male and hermaphrodite ones respectively. Obsrvations on our own material and data from the literature lead us to the conclusion that no such sharp distinction could be made. In this respect especially the hypothesis ofHeslop-Harrison (1957) on the role of auxin in sex determinations is of interest. It is argued that the sex-determing genes together provoke in flower primordia a certain net auxin activity that determines the development of the sex organs. A genothype that realizes a relatively high net auxin activity will favour the develoment of pistils and will work against the formation of stamina. A genotype that causes a relatively low auxin activity has the opposite effect. Changes of distinctly different sex-determining genes might have a similar effect on sex-expression. For example changes of genes in the Y-chromosome of an XY plant may cause the development of a pistil in the flowers of an XY plant and simultaneously work against the formation of stamina, as is demonstrated by some mutations in ourMelandrium material. In one mutation cytologically no aberration of the Y-chromosome was observed. The Y-chromosome of the other mutations appered to lack a part of their non-homologous arms. We observed the same phenotypical change after autosomal selection started in threeM. dioicum populations. A new feature of the distal part of the non-homologous arm of the Y-chromosome showed up in our hermaphrodite gerontogones. This part appeared to be indispensable for the functioning of both female and male gametes. In the discussion the formation of unisexual flowers in monoecious species and in dioecious ones was regarded to be fully comparable. In both instances auxin was assumed to play a dominant part in the differentiation of the flowers. We discussed the possible role of auxin in the regulating mechanism of protein synthesis. The origin of dioecism was explaned in terms of building up an uneven distribution of + genes (increasing the net auxin activity) and-genes (decreasing the net auxin activity) in a non-homologous pair of chromosomes. It is suggested that apomictic plants are like female plants characterized by a relatively high auxin activity in the flower primordia. We assumed therefore apomixis and dioecism to be by their origin related phenomena. With regard to the discrepancy in occurrence of dioecism and polyploidy in the plant kingdom and in the animal kingdom, it is argued that in plant species polyploidisation interferes with the building up of the balanced dioecious system, a situation not met with in the animal kingdom, because of the unfavourable aspects of polyploidy in animals.     

Genetic studies in south Balkan populations

Within a study of the genetics of Balkan populations, four DNA-STR systems and 19 classical markers were examined in seven samples: Romanians (two groups), Albanians, Greeks and Aromuns (three groups). The results for the DNA-STR systems have been compared with data from the literature. The results show four clear separated groups: sub-Saharan black populations, North-African, Japanese and European populations. The large Balkan populations, except the Greek sample, are genetically more homogenous than the Aromun populations. A second Neighbor-joining tree based on all 23 analyzed systems, show a particular trend of the Aromun groups, which indicates a particular genetic structure.     

Conformational studies of bacterial polysaccharides. II. Optical activity of some bacterial capsular polysaccharides

The optical activity of the Klebsiella capsular polysaccharides of serotypes K1, K5, K6, K8, K11, K56, and K57 has been studied in aqueous solution. Measurements of ORD in the range 185–450 nm reveal anomalous ORD with Cotton effects near λ₀ = 195nm. The results are evaluated quantitatively according to hte Moffitt-Yang and the Drude equations. Straight lines are obtained in the Moffitt-Yang plots, while the corresponding Drude plots yield bent curves. The b₀ values, calculated from the slope of the stright lines in the Moffitt-Yang plot, range from 90 to 270 and suggest a helical superstructure for the capsular polysaccyharides. Positive b₀ values have been found for K1, K5, and K6 and negative b₀ values for K8, k11, K56, ad K57. Circular dichrosim has been mesured, but the CD curves are found to be truncated at the lower-wavelength end due to the 185-nm limit of the spectrometer used. Measurements of the temperature dependence of the specific optical rotation [α] reveal in all cases cooperative order–disorder transitions at temperatures, T_m, fro m298 to 323°K. The van′t Hoff enthalpies derived from the width of the transition curves are found to be similar in value to those of polypeptieds in aqueous solution. The K8 polysaccharide shows a two-step transition. The results are discussed in relation to the known primary structure and x-ray data from oriented and partially crystalline films. A model is suggested for the two-step transition in the K8 polysaccharide.