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E Zouros

Publications and source records attributed to E Zouros.

At least 37 records · Page 2Linked to original sources
PubMed1996

Incompatibilities between Y chromosome and autosomes are responsible for male hybrid sterility in crosses between Drosophila virilis and Drosophila texana.

Crosses between Drosophila virilis and D. texana produce viable and fertile F1 males and females. When F1 males are backcrossed to either parental species they also produced fertile sons. However, about one-third of F1 males carrying the D. texana Y chromosome are sterile. When fertile F1 males with the D. texana Y chromosome are crossed to D. virilis, about three quarters of the sons are sterile. We show that these sterilities result from incompatibilities between the D. texana Y chromosome and at least two of the D. virilis autosomes. X/Y incompatibilities can be excluded in this pair of species, and X/autosome incompatibilities appear to be either absent or to play a minor role in the sterility of male progeny from backcrosses of F1 males to females from either species. It is suggested that Y/autosome incompatibilities may be among the first to appear in the development of postzygotic isolation in Drosophila.

Animals↗
PubMed1996

Degree of selective constraint as an explanation of the different rates of evolution of gender-specific mitochondrial DNA lineages in the mussel mytilus.

Mussels of the genus Mytilus segregate for a maternally transmitted F lineage and a paternally transmitted M lineage of mitochondrial DNA. Previous studies demonstrated that these lineages are older than the species of the M. edulis complex and that the M lineage evolves faster than the F lineage. Here we show that the latter observation also applies to a region of the molecule with no assigned function. Sequence data for the mitochondrial COIII gene and the "unassigned" region of the F and M lineages of M. edulis and M. trossulus are used to evaluate various hypotheses that may account for the faster rate of evolution of the M lineage. Tests based on the proportion of synonymous and nonsynonymous substitutions suggest that the M lineage experiences relatively relaxed selection. Further support for this hypothesis comes from an examination of COIII amino acid substitutions at sites defined as either conserved or variable based on the pattern of variation in other mollusks and Drosophila. Most substitutions in the M lineage occur in regions that are also variable among non-Mytilus taxa. We suggest that these differences in selection pressure are a consequence of doubly uniparental mitochondrial DNA transmission in Mytilus.

Amino Acid Sequence↗
PubMed1996

Species-specific segregation of gender-associated mitochondrial DNA types in an area where two mussel species (Mytilus edulis and M. trossulus) hybridize.

In each of the mussel species Mytilus edulis and M. trossulus there exist two types of mtDNA, the F type transmitted through females and the M type transmitted through males. Because the two species produce fertile hybrids in nature, F and M types of one may introgress into the other. We present the results from a survey of a population in which extensive hybridization occurs between these two species. Among specimens classified as "pure" M. edulis or "pure" M. trossulus on the basis of allozyme analysis, we observed no animal that carried the F or the M mitotype of the other species. In most animals of mixed nuclear background, an individual's mtDNA came from the species that contributed the majority of the individual's nuclear genes. Most importantly, the two mtDNA types in post-F1 male hybrids were of the same species origin. We interpret this to mean that there are intrinsic barriers to the exchange of mtDNA between these two species. Because such barriers were not noted in other hybridizing species pairs (many being even less interfertile than M. edulis and M. trossulus), their presence in Mytilus could be another feature of the unusual mtDNA system in this genus.

Animals↗
PubMed1996

Mitochondrial DNA phylogeny and the reconstruction of the population history of a species: the case of the European anchovy (Engraulis encrasicolus).

Analysis of mitochondrial DNA restriction fragment length polymorphism in European anchovy (Engraulis encrasicolus) revealed a large number of mitotypes that form two distinct clusters (phylads). Phylad A consists of one common mitotype and many rare secondary mitotypes that are one mutational step removed from the main type. Nucleotide diversity and number of homoplasious changes are low. Phylad B has a complex pattern of mitotype connectedness, high nucleotide diversity, and a large number of homoplasious changes. It is suggested that the two phylads evolved in isolation from each other and that present coexistence is the result of a secondary contact. Moreover, phylad A has a "star" phylogeny, which suggests that it has evolved in a population that experienced a drastic bottleneck followed by an explosion of size. Phylad A is practically the only phylad present in the Black Sea, with its frequency dropping to 85% in the northern Aegean, and to 40% in the rest of Mediterranean and the Bay of Biscay. The Black Sea is, therefore, the most likely place of origin of phylad A. Molecular data are consistent with a population bottleneck in the Black Sea during the last glaciation event and a subsequent exit of phylad A with the outflow into the Aegean following the ice melting. Phylogenetic analysis of anchovy mtDNA provides a reconstruction of population history in the Mediterranean, which is consistent with the geological information.

Animals↗
PubMed1995

Male and female mitochondrial DNA lineages in the blue mussel (Mytilus edulis) species group.

In blue mussels of the Mytilus edulis species complex, mitochondrial DNA (mtDNA) inheritance is coupled with gender. Females receive their mother's mtDNA and pass it on to both their daughters and sons. In addition, males receive mtDNA from their father and transmit this male mtDNA to their sons. If this pattern of "doubly uniparental inheritance" is older than the M. edulis species complex, then all members of this group must have two distinct mtDNA lineages: a maternal lineage that is transmitted through females and a paternal lineage that is transmitted through males. To test this hypothesis, we scored mtDNA variation in two taxa in this complex, M. edulis and M. trossulus, by means of restriction fragment profiles of whole-mtDNA genomes and DNA sequence of a region of the cytochrome c oxidase subunit III gene (COIII). The various mitotypes present in these mussels were classified as "male" or "female" based on their gender association and as belonging to M. edulis or M. trossulus based on species-specific allozymes. Both maximum parsimony and neighbor-joining phylogenies based on the COIII sequences grouped female and male mtDNAs into two distinct lineages irrespective of specific origin in accordance with the hypothesis that the origin of these lineages predates the divergence of M. edulis and M. trossulus.

Animals↗
PubMed1995

Mitochondrial DNA variation in an experimental stock of gilthead sea bream (Sparus aurata).

We present a restriction site map for the mitochondrial DNA of the gilthead sea bream and the consensus sequence for a region of the mitochondrial cytochrome b gene. Restriction site and nucleotide sequence analysis was used to obtain individual mitotype profiles in a broodstock used for genetic studies. Eight mitotypes were detected among 33 animals assayed. In combination with hypervariable nuclear markers, this variation can be used to identify the parents of any offspring in mass matings and, also, to determine which of the two parents donated the egg and who donated the sperm. On the basis of restriction site variation, the Greek stock analyzed here is very similar to an Israeli stock described in an earlier publication. It is not known if this similarity will hold when the Israeli stock is examined for sequence variation.

Amino Acid Sequence↗
PubMed1994

An unusual type of mitochondrial DNA inheritance in the blue mussel Mytilus.

In animals, mitochondrial DNA (mtDNA) inheritance is predominantly maternal. In a few cases incidental transmission of paternal mtDNA was observed and estimated to account for only 10(-4)-10(-3) of an individual's mtDNA content. In contrast, biparental inheritance is common in mussels of the genus Mytilus. Here we present direct evidence that sex and mtDNA inheritance are coupled in Mytilus. Females inherit mtDNA only from their mother, but they transmit it to both daughters and sons. Males inherit mtDNA from both parents, but they transmit to sons only the mtDNA they inherited from their father. In pair matings, this mtDNA inheritance pattern is associated with a strong sex-ratio bias. These findings establish a newly discovered type of cytoplasmic DNA transmission. We also present evidence that the phenomenon breaks down in interspecific hybrids.

Aging↗
PubMed1994

Allozyme and RFLP heterozygosities as correlates of growth rate in the scallop Placopecten magellanicus: a test of the associative overdominance hypothesis.

Several studies have reported positive correlations between the degree of enzyme heterozygosity and fitness-related traits. Notable among these are the correlations between heterozygosity and growth rate in marine bivalves. Whether the correlation is the result of intrinsic functional differences between enzyme variants at the electrophoretic loci scored or arises from non-random genotypic associations between these loci and others segregating for deleterious recessive genes (the associative overdominance hypothesis) is a matter of continuing debate. A prediction of the associative overdominance hypothesis, not shared by explanations that treat the enzyme loci as causative agents of the correlation, is that the correlation is not specific to the type of genetic marker used. We have tested this prediction by scoring heterozygosity at single locus nuclear restriction fragment length polymorphisms (RFLPs) in a cohort of juvenile scallops (Placopecten magellanicus) in which growth rate was known to be positively correlated with an individual's degree of allozyme heterozygosity. A total of 222 individuals were scored for their genotypes at seven allozyme loci, two nonspecific protein loci of unknown function and eight nuclear RFLPs detected by anonymous cDNA probes. In contrast to the enzyme loci, no correlation was observed between growth rate and the degree of heterozygosity at the DNA markers. Furthermore, there was no relationship between the magnitude of heterozygote deficiency at a locus and its effect on the correlation. The differences observed between the effects of allozyme and RFLP heterozygosity on growth rate provide evidence against the associative overdominance hypothesis, but a strong case against this explanation must await corroboration from similar studies in different species.

Animals↗
PubMed1993

Dispersed discrete length polymorphism of mitochondrial DNA in the scallop Placopecten magellanicus (Gmelin).

Three separate regions exhibiting incremental length polymorphism have been found in the mitochondrial genome of the scallop Placopecten magellanicus. Each locus has a discrete and different unit of variation, measuring 1450 bp at locus I, 250 bp at locus II, and less than 100 bp at locus III. At least six size classes were observed at each locus, and individual variation can account for the intraspecific mtDNA size range of 31-42 kb, but not for the unusually large base size of the genome. Intramolecular hybridization patterns with clones of two of the variable regions indicate that there is a dispersed sequence similarity with the 1,450-bp locus-I repeat and its flanks, and with some part of locus II.

Animals↗
PubMed1993

An autosomal factor from Drosophila arizonae restores normal spermatogenesis in Drosophila mojavensis males carrying the D. arizonae Y chromosome.

Males of Drosophila mojavensis whose Y chromosome is replaced by the Y chromosome of the sibling species Drosophila arizonae are sterile. It is shown that genetic material from the fourth chromosome of D. arizonae is necessary and sufficient, in single dose, to restore fertility in these males. In introgression and mapping experiments this material segregates as a single Mendelian factor (sperm motility factor, SMF). Light and electron microscopy studies of spermatogenesis in D. mojavensis males whose Y chromosome is replaced by introgression with the Y chromosome of D. arizonae (these males are symbolized as mojYa) revealed postmeiotic abnormalities all of which are restored when the SMF of D. arizonae is co-introgressed (these males are symbolized as mojYaSMFa). The number of mature sperm per bundle in mojYaSMFa is slightly less than in pure D. mojavensis and is even smaller in males whose fertility is rescued by introgression of the entire fourth chromosome of D. arizonae. These observations establish an interspecific incompatibility between the Y chromosome and an autosomal factor (or more than one tightly linked factors) that can be useful for the study of the evolution of male hybrid sterility in Drosophila and the genetic control of spermatogenesis.

Animals↗
PubMed1992

Direct evidence for extensive paternal mitochondrial DNA inheritance in the marine mussel Mytilus.

Inheritance of mitochondrial DNA in animals was thought to be strictly maternal. Recently, evidence for incidental paternal mtDNA leakage was obtained in hybrid crosses of Drosophila and mice. In mice, the frequency of paternal mtDNA contributions was estimated at 10(-4), compared with maternal contributions. The common occurrence in the marine mussel Mytilus of heteroplasmic individuals with two or more types of highly diverged mtDNA molecules was interpreted as strong evidence for biparental mtDNA inheritance by some, but not by others. We report here results from pair-matings involving two species of mussels, Mytilus edulis and Mytilus trossulus. Extensive contribution of paternal mtDNA, amounting to several orders of magnitude higher than that inferred for Drosophila or mice, was observed in both intra- and interspecific crosses.

Alleles↗
PubMed1990

Molecular characterization of a repeat element causing large-scale size variation in the mitochondrial DNA of the sea scallop Placopecten magellanicus.

The scallop Placopecten magellanicus has the largest reported animal mitochondrial DNA (average 35 kb) and exhibits large inter- and intraindividual length variation owing to the varying copy number of a repeated element. We have characterized the repeat array by using restriction mapping and sequence analysis. The repeated element consists of 1,442 bp flanked on either side by the sequence ACTTTCC in a direct orientation. The array contains two to eight copies of the repeated element arranged in a direct orientation and in tandem. Only complete copies of the element are present in the array. The repeat element contains three regions with characteristic nucleotide sequences: a 10-bp inverted repeat shown to extrude into a cruciform in a supercoiled DNA plasmid, a 120-bp tract rich in G/C (70%) and adjacent to the inverted repeat, and periodically interspersed homopolymer runs of A and T occurring near the middle of the element which induce DNA curvature in dimeric constructs of the element. The element appears to be unique to P. magellanicus. The structural properties of the repeat element and its organization in an array of repeats may be important in explaining the generation and maintenance of large-scale mitochondrial DNA size variation observed in many animal species.

Animals↗
PubMed1989

Advances in the genetics of reproductive isolation in Drosophila.

Speciation genetics is defined as the study of genetic events and processes that differentiate the probabilities that genetic material from individual members of a population will co-occur in individuals of some future generation. It follows that phenotypic attributes that contribute to this differentiation of probabilities (e.g., mating preferences, sterility, or infertility of individuals from certain types of matings) constitute the phenotype of speciation, and genetic loci that may affect these phenotypic attributes can be considered as speciation genes. The literature on genetic differences between hybridizable species of Drosophila that are responsible for morphological differences, mating preferences, hybrid inviability, and hybrid sterility are reviewed with special reference to the species pair D. mojavensis - D. arizonensis. The case for the involvement of karyotypic changes in speciation in rodents is briefly discussed. It is concluded that no major advance has been made in the speciation genetics of Drosophila since Dobzhansky initiated the field 40 years ago. Yet, the identification of several gene loci that cause hybrid inviability or sterility may open the way to the understanding of reproductive isolation at the molecular level. It is not clear whether this approach will lead to general molecular mechanisms underlying the speciation process.

Animals↗
PubMed1988

Location of an autosomal factor causing sterility in Drosophila mojavensis males carrying the Drosophila arizonensis Y chromosome.

Drosophila mojavensis males whose Y chromosome is replaced by the Y of D. arizonensis, have immotile sperm. Sperm motility is restored if one member of the fourth autosome pair is also replaced by an arizonensis homologue. We present evidence that the effect of the fourth chromosome is due to a single Mendelian factor and map this factor relative to the two markers available for this chromosome. This is an essential first step towards understanding the nature of the incompatibility between the arizonensis Y chromosome and the mojavensis fourth chromosome responsible for this type of post-zygotic isolation between these closely related species.

Animals↗
PubMed1987

Atypical mitochondrial DNA from the deep-sea scallop Placopecten magellanicus.

The mitochondrial DNA of most metazoan animals is highly conserved in size, averaging about 17 kilobase paris (kbp). The mitochondrial DNA from the deep-sea scallop Placopecten magellanicus, in contrast, has been found to be approximately 34 kbp long. It is also highly variable in size from individual to individual and is unusual in the extent of its size variation. Mitochondrial DNAs from individuals collected at the same site differ by as much as 7 kbp. The size variation is due largely to differences in the number of copies of a tandemly repeated 1.2-kbp element.

Journal Article↗