Search results for "Biological evolution"

Chronology for the Cueva Victoria fossil site (SE Spain): Evidence for Early Pleistocene Afro-Iberian dispersals

2014

Cueva Victoria has provided remains of more than 90 species of fossil vertebrates, including a hominin phalanx, and the only specimens of the African cercopithecid Theropithecus oswaldi in Europe. To constrain the age of the vertebrate remains we used paleomagnetism, vertebrate biostratigraphy and (230)Th/U dating. Normal polarity was identified in the non-fossiliferous lowest and highest stratigraphic units (red clay and capping flowstones) while reverse polarity was found in the intermediate stratigraphic unit (fossiliferous breccia). A lower polarity change occurred during the deposition of the decalcification clay, when the cave was closed and karstification was active. A second polarit…

Microstructure and diversity of the bursa copulatrix wall in Tortricidae (Lepidoptera).

2012

The inner surface and muscle structure of the bursa copulatrix are examined for the first time with Electron Microscopy in some representatives of the family Tortricidae (Lepidoptera). The internal microprotuberances reveal taxon dependent characters unstudied in the Lepidoptera until now. Acanthae occur in almost all taxa studied, whereas ctenidia and papillae are found only in representatives of Tortricinae and Olethreutinae, respectively. Muscles are radially arranged from the signa. Areas of muscle insertion on the bursal wall are not covered by other muscle fibers. Muscle attachments to evaginated areas, e.g. capitulum and diverticulum, suggest an apodeme role for these structures, cor…

DNA chips for yeast biotechnology. The case of wine yeasts.

2002

The yeast Saccharomyces cerevisiae is one of the most popular model organisms. It was the first eukaryote whose genome was sequenced. Since then many functional analysis projects have tried to find the function of many genes and to understand its metabolism in a holistic way. Apart from basic science this microorganism is of great interest in several biotechnology processes, such as winemaking. Only global studies of the cell as a whole can help us to understand many of the technical problems facing winemaking. DNA chip technology is one of the most promising tools for the analysis of cell physiology. Yeast has been the model organism for the development of this technique. Many of the studi…

Structure and expression of clustered P element homologues in Drosophila subobscura and Drosophila guanche

1995

Abstract Sequence relationships and functional aspects were analysed in the P element homologues of Drosophila subobscura (Ds) and D. guanche (Dg) . In both species, the P homologues are clustered at a single genomic position. They lack the characteristic terminal structures of actively transposing P elements, but they have the coding capacity for a 66-kDa ‘repressor-like’ protein. Two different types of cluster units (G-type and A-type) can be distinguished. The A-type unit, which is present in multiple copies, is transcribed in adult flies. In contrast, the G-type unit has a much lower copy number and is apparently not expressed. In Dg , the isolated G-type sequence carries a 420-bp inser…

The sex determining region of Chironomus thummi is associated with highly repetitive DNA and transposable elements.

1993

The dominant male sex determiner in chromosome III of the midge Chironomus thummi thummi is closely linked to a large cluster of tandem-repetitive DNA elements, the Cla elements, which are otherwise highly repetitive and distributed over more than 200 sites on all chromosomes. Chromosome III displays a hemizygous cluster of Cla elements in males but not in females. The chromosomal location of this hemizygous Cla element cluster is in the region of the male determiner M as localized by cytogenetic analysis. With Cla elements as hybridization probe, it was possible to clone a large part of the sex determining region. Molecular analysis of the DNA of males and females in this region displayed …

The evolutionary genetics of the hobo transposable element in the Drosophila melanogaster complex.

1994

Hobo elements are a family of transposable elements found in Drosophila melanogaster and its three sibling species: D. simulans, D. mauritiana and D. sechellia. Studies in D. melanogaster have shown that hobo may be mobilized, and that the genetic effects of such mobilizations included the general features of hybrid dysgenesis: mutations, chromosomal rearrangements and gonadal dysgenis in F1 individuals. At the evolutionary level some hobo-hybridizing sequences have also been found in the other members of the melanogaster subgroup and in many members of the related montium subgroup. Surveys of older collected strains of D. melanogaster suggest that complete hobo elements were absent prior t…

Signals of major histocompatibility complex overdominance in a wild salmonid population

2009

The major histocompatibility complex (MHC) contains the most variable genes in vertebrates, but despite extensive research, the mechanisms maintaining this polymorphism are still unresolved. One hypothesis is that MHC polymorphism is a result of balancing selection operating by overdominance, but convincing evidence for overdominant selection in natural populations has been lacking. We present strong evidence consistent with MHC-specific overdominance in a free-living population of Arctic charr (Salvelinus alpinus) in northernmost Europe. In this population, where just two MHC alleles were observed, MHC heterozygous fish had a lower parasite load, were in better condition (as estimated by a…

1993

This quote by J. Huxley reflects the present consensus between scientists, philosophers, and theologians alike, after a long period of fundamental disagreement on this crucial question for mankind.

Is the Quasispecies Concept Relevant to RNA Viruses?

2002

The study of RNA virus evolution has blossomed over the last 20 years. Despite the emergence of this new discipline, there has been little active debate over perhaps the most fundamental question of all. Do RNA viruses evolve in a manner that is qualitatively different from other life forms? For

Two interconnected functional systems in the amygdala of amniote vertebrates.

2008

The amygdala shows ventropallial and lateropallial derivatives that can be compared among vertebrates according to their topological position, either superficial (cortical amygdala) or deep (basolateral amygdala and amygdalo-hippocampal area), connections and histochemical features. On the other hand, the subpallial amygdala, also called extended amygdala, is composed of medial and central divisions. In mammals, both divisions consist of an intra-amygdaloid portion and a part of the bed nucleus of the stria terminalis. In non-mammals, the intratelencephalic trajectory of the stria terminalis is short and both poles of the extended amygdala are close together. Like its mammalian counterpart,…