Let W be an arbitrary Coxeter group, possibly of infinite rank. We describe a decomposition of the centralizer ZW (WI) of an arbitrary parabolic subgroup WI into the center of WI , a Coxeter group and a subgroup defined by a 2-cell complex. Only information about finite parabolic subgroups is required in an explicit computation. Moreover, by using our description of ZW (WI), we reveal a further...

A recent analysis of high angular resolution NIR imaging and spectroscopic data in conjunction with Plateau de Bure interferometric mm-line observations indicate the presence of a circum-nuclear starburst ring of ∼1.5” (1.5 kpc) diameter in I Zw 1. High angular resolution NIR imaging, using the MPE SHARP camera at the ESO NTT, HST V-band images, as well as NIR spectroscopy with MPE 3D provide a...

Transitions between sex determination systems have occurred in many lineages of squamates and it follows that novel sex chromosomes will also have arisen multiple times. The formation of sex chromosomes may be reinforced by inhibition of recombination and the accumulation of repetitive DNA sequences. The karyotypes of monitor lizards are known to be highly conserved yet the sex chromosomes in t...

Sex in birds is chomosomally based (ZZ male, ZW female), but the mechanism underlying sex determination remains unknown. An unresolved question is whether Z gene dosage plays a role in avian sex determination. DMRT1 is an avian Z-linked gene that shows higher expression in male gonads during embryogenesis and has been proposed as a putative testis-determining gene in birds. The Z-linkage of thi...

In the XX/XY sex-determining system, the Y-linked SRY genes of most mammals and the DMY/Dmrt1bY genes of the teleost fish medaka have been characterized as sex-determining genes that trigger formation of the testis. However, the molecular mechanism of the ZZ/ZW-type system in vertebrates, including the clawed frog Xenopus laevis, is unknown. Here, we isolated an X. laevis female genome-specific...

To better understand the origin, evolution, and extent of life, we seek to determine the minimum flux of energy needed for organisms to remain viable. Despite the difficulties associated with direct measurement of the power limits for life, it is possible to use existing data and models to constrain the minimum flux of energy required to sustain microorganisms. Here, a we apply a bioenergetic m...

Many animal taxa show frequent and rapid transitions between male heterogamety (XY) and female heterogamety (ZW). We develop a model showing how these transitions can be driven by sex-antagonistic selection. Sex-antagonistic selection acting on loci linked to a new sex-determination mutation can cause it to invade, but when acting on loci linked to the ancestral sex-determination gene will inhi...

For studies investigating the mechanisms underlying the development of allergic conditions such as asthma, noninvasive methodologies for separating airway and parenchymal mechanics in animal models are required. To develop such a method, seven Brown Norway rats were studied on three occasions over a 14-day period. After the baseline measurements, on the third day inhaled methacholine was admini...