Sequence of the supernumerary B chromosome of maize provides insight into its drive mechanism and evolution.

B chromosomes are enigmatic elements in thousands of plant and animal genomes that persist in populations despite being nonessential. They circumvent the laws of Mendelian inheritance but the molecular mechanisms underlying this behavior remain unknown. Here we present the sequence, annotation, and analysis of the maize B chromosome providing insight into its drive mechanism. The sequence assembly reveals detailed locations of the elements involved with the cis and trans functions of its drive mechanism, consisting of nondisjunction at the second pollen mitosis and preferential fertilization of the egg by the B-containing sperm. We identified 758 protein-coding genes in 125.9 Mb of B chromosome sequence, of which at least 88 are expressed. Our results demonstrate that transposable elements in the B chromosome are shared with the standard A chromosome set but multiple lines of evidence fail to detect a syntenic genic region in the A chromosomes, suggesting a distant origin. The current gene content is a result of continuous transfer from the A chromosomal complement over an extended evolutionary time with subsequent degradation but with selection for maintenance of this nonvital chromosome.

Selected mechanical paremeters of women's hair in the Caucasian population.

OBJECTIVE: More parameters have been used for more detailed description of mechanical properties of human hair as a fibre than in analogous studies. All measured samples were taken from five different locations on the heads of 60 women of varied age. METHODS: For each hair, the diameter was determined optically and then the test in the Deform Type 2 testing machine was carried out. Deformation curves were obtained by testing 10 mm long samples up to the rupture point at constant temperature, humidity and constant crossbar speed of 2 mm/min. The curves were processed with software for the calculation of mechanical parameters of the hairs. This specialized software has been designed by us for that purpose. Resulting values were arranged into tables and figures. RESULTS: As far as hair cross-section is concerned, it has been found that for the European population it appears to be rather higher - 86 µm - than indicated in formerly published texts. The 56 µm mentioned in the work of other authors has been observed only utterly exceptionally, in 0.3 % of the population. All quantities studied (except extensibility) display moderate to strong positive skewness in comparison to Gauss distribution. The most marked skewness is seen in the resilience. At the same time, this quantity displays the highest value of non-Gaussian distribution. The elasticity module of 2.3±0.6 GPa is three times lower than the one reported by other authors, yet according to the fact published in our work - which shows unambiguously that the thinner the hair, the higher elasticity module it displays - the value of 7.2 GPa for the 56 µm thick hairs is comparable and it confirms the hypothesis that the cortex, which is responsible for the mechanical strength of the hair, is contained in a higher ratio in thinner hairs. This similarly applies to the ultimate strength; the linearity limit is hard to compare with literature, as it almost does not appear there. CONCLUSION: By measuring 886 samples from the heads of 60 adult women of European type, it was possible to ascertain the current norm for a larger number of mechanical parameters of the hairs. Further merit of this work is the fact that the hairs were taken systematically from five well-defined places of the studied heads in equal count, which is an aspect formerly published works do not respect and they do not present the location of sampling.

Changes in the mechanical parameters of hair in a group of women in reproductive age.

OBJECTIVE: Hair quality and scalp characteristics are considered to be a significant marker of health. This marker is reflected in mechanical properties of hair. To investigate these properties, hair samples have been collected among women of different age and then analyzed. The thickness, Young's modulus of elasticity and ultimate strength limit were the main observed parameters. METHODS: The diameter of each hair has been measured using an optical microscope equipped with a digital camera. The hair was then clipped into the uniaxial tensile testing device. Each sample has been stretched to failure at a speed of 2 mm/min and force vs. elongation was recorded. The mechanical results were converted with respect to the diameter and Stress-Strain curve was obtained for each sample. In addition, all the analyzed samples were divided into two groups in dependence on the age, namely samples from women younger than 35 and over 35 years of age. All the measured parameters were statistically evaluated. RESULTS: Young's modulus, yield and elongation parameters showed no significant difference among samples. On the other hand there was a significant difference among the samples in ultimate strength values. Findings from group analysis showed that women under 35 years show about 5 times greater variability in hair strength than that of women above that age. CONCLUSION: The results of our study indicate that hair tendency to grow persists up to 30 years of age, then slowly decreases and then achieves a steady state around 60 years of age.