Prevalence of mitochondrial DNA haplogroups in an Australian population.

Mitochondrial DNA (mtDNA) haplogroups are 'neutral polymorphisms' in the mtDNA genome, which have accumulated and persisted along maternal lineages as the human population has migrated worldwide. Three ethnically distinct lineages of human mtDNA populations have been identified: European, characterized by nine haplogroups H, I, J, K, T, U, V, W and X; African, characterized by superhaplogroup L and Asian, characterized by superhaplogroup M. We studied the prevalence of mtDNA haplogroups in participants of the Blue Mountains Eye Study, a large population-based survey of vision conducted between 1991 and 2000 of non-institutionalized permanent residents aged 49 years or older from two suburban postcode areas, west of Sydney, Australia. Total DNA isolated from either hair follicles or blood was available for 3377 of the 3509 participants (96.2%) to determine mtDNA haplogroups by polymerase chain reaction/restriction fragment length polymorphism analysis. Approximately 94.2% of samples could be assigned to one of the nine major European haplogroups, whereas a further 1.2% included the African (L) and Asian (M) superhaplogroups. The five principal haplogroups represented were H (42.9%), U (14.1%), J (10.7%), T (9.2%) and K (8.1%), which together included 85% of this population.

Comparison of single-phase and high-frequency generators for x-ray units.

The purpose of this study was to compare characteristics and performances between single-phase (SP) and high-frequency (HF) generators for x-ray units dedicated to veterinary radiology practice. A 30-kW SP and a 30-kW high HF generator connected to a rotating anode x-ray tube were used for the study. Source-film distance, screen/film combination, and film processing were kept the same during the experiment. The mAs value yielding a similar film optical density of a stair step phantom, as assessed by a densitometer and a similar dose, as assessed by a solid state detector, was estimated for different kVp values. The ratio of the mAs used with the SP generator to the equivalent mAs used with the HF generator to produce similar film density or radiation dose was calculated. Subject contrast was measured for different kVp values as the relative difference in film optical density between two steps of the phantom. The waveform of the tube current was recorded for the two generators using an oscilloscope. Motion artifact was produced on a lateral radiograph of a canine tarsus using the two generators. Reproducibility was assessed by comparing the variances of film density measurements made on the central step of the phantom on 10 consecutive images produced with the two generators. mAs ratios (SP/HF) to obtain similar film optical density ranged from 2 (for 90kVp) to 2.5 (for 70 kVp), and mAs ratios to obtain similar radiation dose ranged from 1.2 (for 100 kVp) to 1.4 (for 70 kVp). Image contrast was slightly higher for the SP than for the HF generator. Current waveform for the SP generator was half-sinusoidal and it was almost continuous for the HF generator. Motion artifact appeared as blur for the HF generator and as several regularly placed images of the subject for the SP generator. Reproducibility was significantly better for the HF than for the SP generator (P = 0.047). It was concluded that the HF generator was approximately two times more efficient, had a better reproducibility, and produced images with a lower contrast than the SP generator. Motion artifact appears differently due to different current waveform.

Nucleotide sequence of the F plasmid leading region.

The entire nucleotide sequence of the first DNA segment of the conjugative F plasmid to enter the recipient cell, the leading region, is described. Analysis of the sequence provides further evidence that products encoded within the 13.2-kb leading region are likely to be expressed and perform functions associated with the transferred strand in the recipient cell.