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  • 1
    Electronic Resource
    Electronic Resource
    SEX DETERMINATION, SEX RATIOS, AND GENETIC CONFLICT (1998)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 29 (1998), S. 233-261 
    Details
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Genetic mechanisms of sex determination are unexpectedly diverse and change rapidly during evolution. We review the role of genetic conflict as the driving force behind this diversity and turnover. Genetic conflict occurs when different components of a genetic system are subject to selection in opposite directions. Conflict may occur between genomes (including paternal-maternal and parental-zygotic conflicts) or within genomes (between cytoplasmic and nuclear genes or sex chromosomes and autosomes). The sex-determining system consists of parental sex-ratio genes, parental-effect sex determiners, and zygotic sex determiners, which are subject to different selection pressures because of differences in their modes of inheritance and expression. Genetic conflict theory is used to explain the evolution of several sex-determining mechanisms, including sex chromosome drive, cytoplasmic sex-ratio distortion, and cytoplasmic male sterility in plants. Although still limited, there is growing evidence that genetic conflict could be important in the evolution of sex-determining mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ecolsys.29.1.233
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  • 2
    Electronic Resource
    Electronic Resource
    Amazon molly and Muller's ratchet (1995)
    [s.l.] : Nature Publishing Group
    Nature 375 (1995), S. 111-112 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - The Amazon molly, Poecilia for-mosa, is a gynogenetic fish and a hybrid between R mexicana and R latipinna. The all-female R formosa need to mate with males of R mexicana or R latipinna, as parthenogenetic egg development can start only after sperm fusion. It is generally ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/375111c0
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  • 3
    Electronic Resource
    Electronic Resource
    Junctions between repetitive DNAs on the PSR chromosome of Nasonia vitripennis: Association of palindromes with recombination (1994)
    Springer
    Journal of molecular evolution 38 (1994), S. 352-362 
    Details
    ISSN: 1432-1432
    Keywords: Paternal-Sex-Ratio ; Nasonia ; Repetitive DNA ; Junctions ; Recombination ; Palindromes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Paternal-Sex-Ratio (PSR) chromosome of Nasonia vitripennis contains several families of repetitive DNAs that show significant sequence divergence but share two palindromic regions. This study reports on the analysis of junctions between two of these repetitive DNA families (psr2 and psr18). Three lambda clones that hybridized to both repeat families were isolated from PSR-genomic DNA libraries through multiple screenings and analyzed by Southern blots. Analysis of clones showed a region in which the two repeat types are interspersed, flanked by uniform blocks of each repeat type. PCR amplification of genomic DNA confirmed the contiguous arrangement of psr2 and psr18 on PSR and identified an additional junction region between these repeats that was not present in the lambda inserts. We isolated and sequenced 41 clones from the lambda inserts and genomic PCR products containing junction sequences. Sequence analysis showed that all transitions between psr2 and psr18 repeats occurred near one of the two palindromes. Based on the inheritance pattern of PSR, recombination between repeats on this chromosome must be mitotic (rather than meiotic) in origin. The occurrence of exchanges near the palindromes suggests that these sequences enhance recombination between repeat units. Rapid amplification of repetitive DNA may have been an important factor in the evolution of the PSR chromosome.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00163152
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of deletions on mitotic stability of the Paternal-Sex-Ratio (PSR) chromosome from Nasonia (1992)
    Springer
    Chromosoma 102 (1992), S. 20-26 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Paternal-Sex-Ratio (PSR) is a B chromosome that causes all-male offspring in the parasitoid wasp Nasonia vitripennis. It is only transmitted via sperm of carrier males and destroys the other paternal chromosomes during the first mitotic division of the fertilized egg. Because of haplodiploidy, the effect of PSR is to convert diploid (female) eggs into haploid eggs that develop into PSR-bearing males. The PSR chromosome was previously found to contain several families of repetitive DNA, which appear to be present in local blocks. PSR chromosomes with irradiation-induced deletions have decreased rates of transmission and increased variation in transmission. This study investigates whether these differences in transmission of deletion chromosomes are due to mitotic instability. Two deleton chromosomes (E306 and F316) and the wild-type PSR chromosome were examined. A cytogenetic assay of testes revealed that wild-type PSR males contained the chromosome in 98%–100% of their spermatocytes. Similar counts from carriers of two delection chromosomes were lower and varied between individuals from 50%–100%. One F316 male did not contain the chromosome in any of its spermatocytes although the chromosome was present in somatic tissues based on hybridization to PSR-specific repetitive DNA. A molecular analysis of males found the wild-type PSR chromosome to be present in all somatic tissues. Tissue specific differences in the presence of PSR were found in several males from the two deletion lines. The results show that deletions can result in mosaicism due to increased mitotic instability of PSR. Such individuals sometimes partially or completely fail to transmit the chromosome. Patterns of mosaicism of B chromosomes in other organisms are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00352286
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  • 5
    Electronic Resource
    Electronic Resource
    Phenotypic fitness effects of the selfish B chromosome, paternal sex ratio (PSR) in the parasitic waspNasonia vitripennis (1994)
    Springer
    Evolutionary ecology 8 (1994), S. 1-24 
    Details
    ISSN: 1573-8477
    Keywords: B chromosome ; fitness ; Nasonia ; Paternal Sex Ratio ; population genetics ; selfish DNA ; sperm competition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary B chromosomes are often considered genomic parasites. Paternal sex ratio (PSR) is an extreme example of a parasitic B chromosome in the parasitoid waspNasonia vitripennis. PSR is transmitted through the sperm of carrier males and destroys the other paternal chromosomes in early fertilized eggs. PSR disrupts the normal haplodiploid sex determination in this wasp by converting diploid (female) eggs into haploid (male) eggs that bear PSR. In this study I compare a number of phenotypic fitness aspects of PSR and standard (non-PSR) males. In general, PSR males were as fit as standard males. No significant differences were found in longevity (with one exception), ability to compete for mates and sperm depletion rates. PSR males produced 11–22% larger family sizes and developed slightly faster than standard males. Under conditions of sperm competition, females who mated with both types of males fertilized a constant proportion of eggs with each sperm type over their lifetime. PSR males produced fewer offspring among progenies from double-inseminated females. Phenotypic fitness effects are believed to play a minor role in determining PSR frequencies in natural populations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01237662
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  • 6
    Electronic Resource
    Electronic Resource
    Spatial and ecological overlap between coexisting sexual and parthenogenetic Schmidtea polychroa (Tricladida; Platyhelminthes) (1999)
    Springer
    Hydrobiologia 392 (1999), S. 179-185 
    Details
    ISSN: 1573-5117
    Keywords: gene flow ; population ecology ; Dugesia ; Schmidtea ; parthenogenesis ; coexistence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Theoretical models on the costs and benefits of sexual reproduction usually assume that sexual and parthenogenetic individuals coexist and are identical, except for their mode of reproduction. Empirical studies, however, show that conspecific sexuals and parthenogens can differ in ecological preferences and geographical distribution, which complicates the investigation of the costs and benefits of sex. The freshwater planarian Schmidtea polychroa exists in a sexual and a sperm-dependent, parthenogenetic form. The latter produce fertile sperm and mate, but received sperm is used only to induce parthenogenetic embryo development. We compared the spatial and ecological distribution between forms within a lake from which both had been reported. Forty samples showed large differences in the relative frequencies of sexuals and parthenogens. Nineteen samples contained both biotypes. All but one of the 13 ecological parameters that we measured, could not explain a significant part of the variance in relative abundance of each type. Only leech abundance had a significant, negative effect on the presence of sexual individuals. The causes of this effect remained unclear. We also estimated the amount of genetic isolation between sites and between reproductive modes, using body coloration as a genetic marker. Large differences were found between sites, suggesting isolation of local populations by migration barriers. There were smaller differences between sexuals and parthenogens within sites, suggesting that genetic exchange between biotypes may be limited. We conclude that there appears to be weak niche differentiation between sexuals and parthenogens in Lago di Caldonazzo in late summer. Fluctuations in relative frequency appears to be a consequence of low dispersal between local populations and stochastic effects within them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003519418925
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  • 7
    Electronic Resource
    Electronic Resource
    Reproductive modes, ploidy distribution, and supernumerary chromosome frequencies of the flatworm Polycelis nigra (Platyhelminthes: Tricladida) (1998)
    Springer
    Hydrobiologia 383 (1998), S. 277-285 
    Details
    ISSN: 1573-5117
    Keywords: flatworm ; Polycelis ; polyploidy ; pseudogamous parthenogenesis ; supernumerary chromosome ; Tricladida
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The hermaphroditic flatworm, Polycelis nigra, is characterized by two reproductive biotypes which differ with respect to ploidy; sexual individuals are diploid (n = 8, 2× = 16) and pseudogamous parthenogenetic individuals are polyploid (typically 3×). We have collected and karyotyped individuals from 15 sampling sites (13 in mid to northern Italy, one in Great Britain and one in The Netherlands). We found that biotypes can exist alone or in sympatry, and identified purely diploid, mixed diploid-polyploid, and purely polyploid populations. Karyotype data show that in addition to the normal autosome complement, B chromosomes of differing morphology as well as stable aneuploid chromosomes (extra-A) were found almost exclusively in polyploids (11 of 12 sites). We extensively sampled Lago di Toblino (northern Italy), a pure polyploid population characterized by a submetacentric to metacentric, mitotically stable B chromosome, as well as a stable extra-A chromosome. Here, individuals having 1–3 B chromosomes were more abundant (61%) than those having no B's, implying that B chromosome infection has little detrimental effect when occurring in low numbers. Furthermore, 66% of individuals from this population possessed extra-A chromosomes, although it is unclear whether these elements are aneuploid autosomes or B chromosomes of different morphology. The ubiquity of these chromosomes, within asexuals in particular, is suggestive of a correlation between the origination of the elements and the evolution of polyploidy, or may reflect increased tolerance of parthenogenetic genomes to aneuploidy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003460132521
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  • 8
    Electronic Resource
    Electronic Resource
    Abstracts (1998)
    Springer
    Hydrobiologia 383 (1998), S. 329-330 
    Details
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003472304144
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  • 9
    Electronic Resource
    Electronic Resource
    Sex determination in hymenoptera: A need for genetic and molecular studies (1995)
    New York, NY : Wiley-Blackwell
    BioEssays 17 (1995), S. 813-817 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Sex-determining mechanisms appear to be very diverse in invertebrates. Haplodiploidy is a widespread mode of reproduction in insects: males are haploid and females are diploid. Several models have been proposed for the genetic mechanisms of sex determination in haplodiploid Hymenoptera. Although a one-locus multi-allele model is valid for several species, sex determination in other species cannot be explained by any of the existing models. Evidence for and predictions of two recently proposed models are discussed. Some genetic and molecular approaches are proposed to study sex determination in Hymenoptera.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950170911
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  • 10
    Electronic Resource
    Electronic Resource
    Is the Y chromosome of Drosophila an evolved supernumerary chromosome? (1996)
    New York, NY : Wiley-Blackwell
    BioEssays 18 (1996), S. 317-323 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The Y chromosomes of most Drosophila species are necessary for male fertility but they are not involved in sex determination. They have many puzzling properties that resemble the effects caused by B chromosomes. Classical genetic and molecular studies reveal substantial affinities between Y and B chromosomes and suggest that the Y chromosomes of Drosophila are not degenerated homologues of the X chromosomes, but rather that their Y chromosomes evolved as specialized supernumeraries similar to classical B chromosomes.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950180410
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