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Results for “W chromosome evolution”

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PubMed1998

Concerted evolution of members of the multisequence family chAB4 located on various nonhomologous chromosomes.

During the last years it became obvious that a lot of families of long-range repetitive DNA elements are located within the genomes of mammals. The principles underlying the evolution of such families, therefore, may have a greater impact than anticipated on the evolution of the mammalian genome as a whole. One of these families, called chAB4, is represented with about 50 copies within the human and the chimpanzee genomes and with only a few copies in the genomes of gorilla, orang-utan, and gibbon. Members of chAB4 are located on 10 different human chromosomes. FISH of chAB4-specific probes to chromosome preparations of the great apes showed that chAB4 is located, with only one exception, at orthologous places in the human and the chimpanzee genome. About half the copies in the human genome belong to two species-specific subfamilies that evolved after the divergence of the human and the chimpanzee lineages. The analysis of chAB4-specific PCR-products derived from DNA of rodent/human cell hybrids showed that members of the two human-specific subfamilies can be found on 9 of the 10 chAB4-carrying chromosomes. Taken together, these results demonstrate that the members of DNA sequence families can evolve as a unit despite their location at multiple sites on different chromosomes. The concerted evolution of the family members is a result of frequent exchanges of DNA sequences between copies located on different chromosomes. Interchromosomal exchanges apparently take place without greater alterations in chromosome structure.

Animals↗
PubMed1994

Selection on silent sites in the rodent H3 histone gene family.

Selection promoting differential use of synonymous codons has been shown for several unicellular organisms and for Drosophila, but not for mammals. Selection coefficients operating on synonymous codons are likely to be extremely small, so that a very large effective population size is required for selection to overcome the effects of drift. In mammals, codon-usage bias is believed to be determined exclusively by mutation pressure, with differences between genes due to large-scale variation in base composition around the genome. The replication-dependent histone genes are expressed at extremely high levels during periods of DNA synthesis, and thus are among the most likely mammalian genes to be affected by selection on synonymous codon usage. We suggest that the extremely biased pattern of codon usage in the H3 genes is determined in part by selection. Silent site G + C content is much higher than expected based on flanking sequence G + C content, compared to other rodent genes with similar silent site base composition but lower levels of expression. Dinucleotide-mediated mutation bias does affect codon usage, but the affect is limited to the choice between G and C in some fourfold degenerate codons. Gene conversion between the two clusters of histone genes has not been an important force in the evolution of the H3 genes, but gene conversion appears to have had some effect within the cluster on chromosome 13.

Animals↗
PubMed2006

Unique gene structure and paralogy define the 7D-cadherin family.

Cadherins are Ca2+-dependent transmembrane glycoproteins crucial for cell-cell adhesion in vertebrates and invertebrates. Classification of this superfamily due to their phylogenetic relationship is currently restricted to three major subfamilies: classical, desmosomal and protocadherins. Here we report evidence for a common phylogenetic origin of the kidney-specific Ksp- (Cdh16) and the intestine-specific LI-cadherin (Cdh17). Both genes consist of 18 exons and the positions of their exon-intron boundaries as well as their intron phases are perfectly conserved. We found an extensive paralogy of more than 40 megabases in mammals as well as teleost fish species encompassing the Ksp- and LI-cadherin genes. A comparable paralogy was not detected for other cadherin gene loci. These findings suggest that the Ksp- and LI-cadherin genes originated by chromosomal duplication early during vertebrate evolution and support our assumption that both proteins are paralogues within a separate cadherin family that we have termed 7D-cadherins.

Animals↗
PubMed2001

Pathogenicity islands and virulence evolution in Listeria.

As in other bacterial pathogens, the virulence determinants of Listeria species are clustered in genomic islands scattered along the chromosome. This review summarizes current knowledge about the structure, distribution and role in pathogenesis of Listeria virulence loci. Hypotheses about the mode of acquisition and evolution of these loci in this group of Gram-positive bacteria are presented and discussed.

Amino Acid Sequence↗
PubMed2006

Duplication and relocation of the functional DPY19L2 gene within low copy repeats.

BACKGROUND: Low copy repeats (LCRs) are thought to play an important role in recent gene evolution, especially when they facilitate gene duplications. Duplicate genes are fundamental to adaptive evolution, providing substrates for the development of new or shared gene functions. Moreover, silencing of duplicate genes can have an indirect effect on adaptive evolution by causing genomic relocation of functional genes. These changes are theorized to have been a major factor in speciation. RESULTS: Here we present a novel example showing functional gene relocation within a LCR. We characterize the genomic structure and gene content of eight related LCRs on human Chromosomes 7 and 12. Two members of a novel transmembrane gene family, DPY19L, were identified in these regions, along with six transcribed pseudogenes. One of these genes, DPY19L2, is found on Chromosome 12 and is not syntenic with its mouse orthologue. Instead, the human locus syntenic to mouse Dpy19l2 contains a pseudogene, DPY19L2P1. This indicates that the ancestral copy of this gene has been silenced, while the descendant copy has remained active. Thus, the functional copy of this gene has been relocated to a new genomic locus. We then describe the expansion and evolution of the DPY19L gene family from a single gene found in invertebrate animals. Ancient duplications have led to multiple homologues in different lineages, with three in fish, frogs and birds and four in mammals. CONCLUSION: Our results show that the DPY19L family has expanded throughout the vertebrate lineage and has undergone recent primate-specific evolution within LCRs.

Amino Acid Sequence↗
PubMed1994

Structure of homeobox-leucine zipper genes suggests a model for the evolution of gene families.

Homeobox genes are present in both plants and animals. Homeobox-leucine zipper genes, however, have been identified thus far only in the small mustard plant Arabidopsis thaliana. This observation suggests that homeobox-leucine zipper genes evolved after the divergence of plants and animals, perhaps to mediate specific regulatory events. To better understand this gene family, we isolated several sequences containing the homeobox-leucine zipper motif and carried out a comparative analysis of nine homeobox-leucine zipper genes (HAT1, HAT2, HAT3, HAT4, HAT5, HAT7, HAT9, HAT14, and HAT22). Gene structures, sequence comparisons, and chromosomal locations suggest a simple model for the evolution of these genes. The model postulates that a primordial homeobox gene acquired a leucine zipper by exon capture. The nascent homeobox-leucine zipper gene then appears to have undergone a series of gene duplication and chromosomal translocation events, leading to the formation of the HAT gene family. This work has general implications for the evolution of regulatory genes.

Arabidopsis↗
PubMed1995

Linkage mapping in Papio baboons: conservation of a syntenic group of six markers on human chromosome 1.

We have established multipoint genetic linkage among six loci in baboons (Papio hamadryas). Published PCR primers designed to amplify five human microsatellite loci were used to amplify homologous loci in 229 pedigreed baboons. Southern blotting was used to type two RFLPs in a functional gene (anti-thrombin III) in a subset of those animals. All six loci are known to map to human chromosome 1q, a region of the genome predicted by karyotype studies to be conserved in baboons. Pairwise recombination frequencies and lod scores indicate that the six loci are also linked in baboons. Recombination distances among the loci are similar to those reported for humans. Like humans, the baboons exhibit higher rates of recombination in females than in males. This study demonstrates that (1) microsatellite loci first described and characterized in the human genome can be effectively used for genetic linkage mapping in non-human primates, (2) a group of genetic loci known to be linked on human chromosome 1q are also linked in the baboon genome, and (3) sex differences in recombination frequencies among loci on human chromosome 1q are also observed in the genome of this Old World monkey. This constitutes the first reported multipoint linkage map in any nonhuman primate.

Animals↗
PubMed1992

An optimizing principle of natural selection in evolutionary population genetics.

This paper brings together two themes in evolutionary population genetics theory. The first concerns Fisher's Fundamental Theorem of Natural Selection: a recent interpretation of this theorem claims that it is an exact result, relating to the so-called "partial" increase in mean fitness. The second theme concerns the desire to find an optimality principle in genetic evolution. Such a principle is found here: of all gene frequency changes which lead to the same partial increase in mean fitness as the natural selection gene frequency changes, the natural selection values minimize a generalized distance measure between parent and daughter generation gene frequency values.

Alleles↗
PubMed1977

Adaptation at specific loci. I. Natural selection on phosphoglucose isomerase of Colias butterflies: Biochemical and population aspects.

Electrophoretic variants of phosphoglucose isomerase (PGI) in Colias butterflies have been studied from field and laboratory viewpoints. The transmission pattern is that of a dimeric enzyme controlled by one structural gene locus. Populations usually harbor four to six allelic mobility classes. These mobility classes are shared among species complexes, though their frequencies differ widely. Preliminary Ferguson plot analysis of the variants has been carried out. Purified preparations of Colias PGI alleles are more effective in standardizing Ferguson plots than heterologous proteins, such as ferritin. Variation of Ferguson plot parameters is not an infallible guide to electrophoretically "cryptic alleles," as one putative case proved to be due to nonallele-specific effects. S, M, and F mobility classes in two Colias semispecies show the same retardation coefficients in Ferguson plots. Adults early in the flight periods of their nonoverlapping generations show genotype frequencies in Hardy-Weinberg equilibrium, but heterozygote excess develops as the insects age. Simple directional selection and large-scale population mixing are unlikely to be causes of this, although several other selection modes remain possible. Identical-by-descent lines of the four frequent-to-common alleles in C. eurytheme have been set up in culture, and enzyme has been purified from these for study of functional properties. Major differenecs in heat stability and in various kinetic parameters are found among the ten possible genotypes. In some cases, heterosis for kinetic parameters is seen; in other cases, opposing trends in kinetic function and heat stability create potential for net heterosis in function. Possible interpretations of these results in an adaptive metabolic context are discussed, and directions for further work are stated.

Animals↗
PubMed1974

Banded marker chromosomes as indicators of intraspecies cellular contamination.

Chromosome banding revealed marked chromosomes characteristic of HeLa cells in cultures designated HEK, HEK/HRV, HBT-3, HBT-39B, MA160, and a strain of SA-4TxS-Husa(1). Ohter HeLa cell characteristics found were glucose-6-phosphate dehydrogense type A mobility and lack the Y chromosome. Conventional chromosome analysis and immunological and enzymatic technique serve to monitor species specificity and racial origin of the donor. Chromosome banding, however, can monitor intralinear karyotype peculiarity and its evolution during long-term cultivation.

Cell Line↗
PubMed1989

Cytological approaches to simuliid biosystematics in relation to the epidemiology and control of human onchocerciasis.

This paper presents an overview of advances in cytological research on the biosystematics of vector simuliid complexes in the areas of identification, age grading, and the evolution of resistance in relation to the epidemiology and control of human onchocerciasis. Systematic theory is discussed and relevant examples are given to show its application in predicting and resolving current problems in species identification for New World and Old World vector complexes. These complexes include Simulium damnosum s.l. and S. neavei s.l. from Africa and S. exiguum s.l., S. metallicum s.l., S. ochraceum s.l., and S. oyapockense s.l. from Latin America. The evolution of resistance in S. damnosum s.l. and the need for future molecular research as part of resistance management strategies are discussed.

Africa↗
PubMed1992

Synteny mapping in the bovine: genes from human chromosome 4.

Genes homologous to those located on human chromosome 4 (HSA4) were mapped in the bovine to determine regions of syntenic conservation among humans, mice, and cattle. Previous studies have shown that two homologs of genes on HSA4, PGM2 and PEPS, are located in bovine syntenic group U15 (chromosome 6). The homologous mouse genes, Pgm-1 and Pep-7, are on MMU5. Using a panel of bovine x hamster hybrid somatic cells, we have assigned homologs of 11 additional HSA4 loci to their respective bovine syntenic groups. D4S43, D4S10, QDPR, IGJ, ADH2, KIT, and IF were assigned to syntenic group U15. This syntenic arrangement is not conserved in the mouse, where D4s43, D4s10, Qdpr, and Igj are on MMU5 while Adh-2 is on MMU3. IL-2, FGB, FGG, and F11, which also reside on MMU3, were assigned to bovine syntenic group U23. These data suggest that breaks and/or fusions of ancestral chromosomes carrying these genes occurred at different places during the evolution of humans, cattle, and mice.

Animals↗