Sex-dependent selection often leads to spectacularly different phenotypes in males and females. In species in which sexual dimorphism is not complete, it is unclear which benefits females and males derive from displaying a trait that is typical of the other sex. In barn owls (Tyto alba), females exhibit on average larger black eumelanic spots than males but members of the two sexes display this...

Sex-ratio distortion is the most common form of non-Mendelian segregation observed in natural populations. It may occur even more frequently than direct observations suggest, because the dysgenic population consequences of a biased sex ratio are expected to result in the rapid evolution of suppressors, resulting in suppressed or "cryptic" segregation distortion. Here we report evidence for cryp...

Heteropteran insects are characterized by holokinetic chromosomes, and, in most species, the post-reductional meiotic division of sex chromosomes and the presence of one chiasma per bivalent. The Reduviidae have a modal diploid autosomal number of 20 with a range between 12 to 34, and both simple and multiple sex chromosome systems (XY/XX, X0/XX, XnY/XnXn). Within this family cytogenetic report...

BACKGROUND In many species, sex is determined by a system involving X and Y chromosomes, the latter having lost much of their genetic activity. Sex chromosomes have evolved independently many times, and several different mechanisms responsible for the degeneration of the Y chromosome have been proposed. Here, we have taken advantage of the secondary sex chromosome pair in Drosophila miranda to ...

In the present work, we analysed the male meiosis, the content and distribution of heterochromatin and the number and location of nucleolus organizing regions in Microtomus lunifer (Berg, 1900) by means of standard technique, C- and fluorescent bandings, and fluorescent in situ hybridization with an 18S rDNA probe. This species is the second one cytogenetically analysed within the Hammacerinae....

Understanding the maintenance of genetic variation in the face of selection remains a key issue in evolutionary biology. One potential mechanism for the maintenance of genetic variation is opposing selection during the diploid and haploid stages of biphasic life cycles universal among eukaryotic sexual organisms. If haploid and diploid gene expression both occur, selection can act in each phase...

the effect of genotype and sex of nigerian indigenous chickens (dwarf, fulani ecotypes, neck, frizzle and normal feathered) on blood serum electrolytes and biochemical parameters were investigated using 40 chickens. the collected data were subjected to analysis via a 2 way anova. the results revealed serum levels of sodium, potassium, chloride, uric acid, glucose, total protein, creatinin, albu...

Models of sex chromosome and autosome evolution yield key predictions about the genomic basis of adaptive divergence, and such models have been important in guiding empirical research in comparative genomics and studies of speciation. In addition to the adaptive differentiation that occurs between species over time, selection also favors genetic divergence across geographic space, with subpopul...

A family is reported in which three boys, two full brothers and a half brother, presented with marked delay in motor milestones, severe limb and truncal ataxia, nystagmus, speech delay and moderate global retardation. Autosomal recessive and sex linked recessive forms of cerebellar hypoplasia are reviewed and it is suggested that this family may have a rare, if not unique, form of sex-linked ce...