Global Recombination Rate Research Articles

Silencing of unpaired meiotic chromosomes and altered recombination patterns in an azoospermic carrier of a t(8;13) reciprocal translocation

Male carriers of structural chromosomal abnormalities provide a useful model for studying the effects of impaired synapsis on human meioses and male fertility. We used immunofluorescent techniques to examine recombination (MLH1), synapsis (SYCP3/SYCP1) and transcriptional inactivation (BRCA1/gammaH2AX/RNA polymerase II) of meiotic chromosomes in an azoospermic carrier of a t(8;13) reciprocal translocation. Two biopsies were performed 1 year apart and on different testes. Global recombination rates differed between the two biopsies. Although global recombination rates were not altered when compared with control men, recombination frequencies were reduced specifically on the rearranged chromosomes. Asynapsed quadrivalents were observed in 90% and 87% of pachytene nuclei from the first and second biopsies, respectively, and were frequently associated with the sex chromosomes. BRCA1 and gammaH2AX, two proteins implicated in meiotic sex chromosome inactivation, localized along asynapsed regions regardless of whether or not they were associated with the sex chromosomes. Immunostaining for RNA polymerase II provided further evidence that unsynapsed regions are silenced during human meiosis. The fidelity of synapsis is a critical factor in determining the outcome of gametogenesis in humans, as the transcriptional inactivation of asynapsed regions may silence meiotic genes, leading to meiotic arrest and infertility.

Determination of the global recombination rate coefficient for the ISX-B tokamak

The global recombination rate coefficient for hydrogen has been measured for the ISX-B tokamak vacuum vessel for various surface conditions. The measurements were performed by observing the rate of decrease of gas pressure in the vessel during a glow discharge. The parameters of the glow discharge and the complete experimental method are described. Previously published analytic and numerical models are used for data analysis. The effects of surface contamination on the results are described. For “unclean” wall conditions σk r = 1.8 × 10 −28 cm 4/atom·s at 296 K and increases to σk r = 4.4 × 10 −28 cm 4/atom·s for “clean” conditions and remains constant until subsequent exposure to air.