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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of Hybrid Zones (1985)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 16 (1985), S. 113-148 
    Details
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.es.16.110185.000553
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  • 2
    Electronic Resource
    Electronic Resource
    Adaptation, speciation and hybrid zones (1989)
    [s.l.] : Nature Publishing Group
    Nature 341 (1989), S. 497-503 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Many species are divided into a mosaic of genetically distinct populations, separated by narrow zones of hybridization. Studies of hybrid zones allow us to quantify the genetic differences responsible for speciation, to measure the diffusion of genes between diverging taxa, and to understand the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/341497a0
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  • 3
    Electronic Resource
    Electronic Resource
    Stock composition in North Atlantic populations of whiting using microsatellite markers (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 51 (1997), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A size-selected library constructed from DNA of the whiting Merlangius merlangus was screened. From about 3200 recombinant clones, 43 microsatellite loci were detected. Thirteen were sequenced in full. Primers were designed from the sequence of the flanking regions for six loci and used to test the allelic variability at these loci using the polymerase chain reaction (PCR). In addition, five primer pairs developed for the stickleback and another seven for cod were tested. Only six primer pairs revealed at least three alleles per locus. The three useful loci Gmo2, Mmer-UEAW01 and Mmer-UEAW02, had 14–23 alleles per locus in 370 samples. Estimates of genetic structure (φ) were not statistically significant. However, estimates of genetic differentiation (Fst) were significantly different from zero. Heterogeneity χ2-analysis of allele frequencies among populations suggested relatively low levels of differentiation among samples. Significantly different allele frequency distributions were found for Borgensfjord and northern and southern North Sea samples for at least one locus, and between the latter samples for Mmer-UEAW02 and Gmo2. There were significant excesses of homozygotes in all samples, over expectation for randomly mating populations in Hardy-Weinberg equilibrium. The estimated frequencies of null alleles were 14.3%, for Mmer-UEAW01, 10.2% for Mmer-UEAW02 and 11.6% for Gmo2. This result calls for a careful interpretation of the significance of these microsatellite data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1997.tb01504.x
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  • 4
    Electronic Resource
    Electronic Resource
    Karyotype stability and DNA variability in the Acrididae (1966)
    Springer
    Chromosoma 20 (1966), S. 155-172 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The Acrididae are frequently quoted as one of the classic examples of karyotypic stability. Within the family, the Cryptosacci, for instance, are characterised by a majority of species having 23 chromosome arms in the male. The members are then related by Robertsonian sequences in which the basic karyotype is believed to consist of 23 acrocentric elements. Thus the 17-chromosome complement of male truxalines is argued to have been derived from the basic type by three successive centric fusions. Such an origin is at variance with the fact that the rod-shaped chromosomes in eight of the nine species utilised in this study turn out in fact to be telocentric. The scheme is also at variance with the finding that significant differences in DNA content exist both between species within the same chromosome group and between member species of the 17 and 23 groups. The concept of karyotypic stability is thus called to question and the relationship of karyotypes within the family must be considerably more complex than has formerly been supposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335205
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  • 5
    Electronic Resource
    Electronic Resource
    Patterns and pathways of chromosome evolution within the Orthoptera (1968)
    Springer
    Chromosoma 25 (1968), S. 40-74 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A series of case histories are provided which confirm the occurrence of telocentric chromosomes within the Orthoptera. These cases necessitate a fairly radical revision of ideas concerning the principles governing chromosome rearrangement within this group. They also challenge several of the dogmas upon which chromosome evolution has in the past been predicated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338233
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  • 6
    Electronic Resource
    Electronic Resource
    The B-chromosome system of myrmeleotettix maculatus (Thunb.) (1965)
    Springer
    Chromosoma 17 (1965), S. 121-138 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary 1. B-chromosomes of two morphological types (Bm and Bsm) have been detected in 27 out of 31 populations of Myrmeleotettix maculatus collected from the southern half of Britain during the summer of 1964. In Wales and central England only B -type chromosomes are represented but along the south coast a majority of populations contain mixtures of the two types. 2. Individuals with B-chromosomes occur in the population with frequencies ranging from 15 to 70% though in 19 of the 27 populations where they were present the frequency value lay between 30 and 50%. 3. Various combinations of from 1 to 3 B-chromosomes have been recovered within B-containing populations. The only two 3B-containing individuals which we have found proved to be germ-line mosaics containing a proportion of cells with only 2 B's. All the other individuals were mitotically stable. 4. Diplotene chiasma scores from 10 individuals in each of 22 of the 31 populations collected were significantly different even when the scores of individuals with B-chromosomes were omitted from the analysis. B-chromosomes do, however, tend to increase both the mean chiasma frequency and the within-individual variation of chiasma frequency in individuals possessing them when these are compared with non-B individuals from the same population. With respect to these increases it appears to make no difference whether an individual carries one or two B-chromosomes or whether the Bm or the Bm type is involved. 5. No correlation exists between the percentage of individuals with B-chromosome in a population and its chiasma frequency level. But the chiasma frequency of individuals with B-chromosomes is positively correlated with that of individuals lacking B-chromosomes from the same population.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330078
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  • 7
    Electronic Resource
    Electronic Resource
    Parallel polymorphism for supernumerary segments inChorthippus parallelus (zetterstedt) (1968)
    Springer
    Chromosoma 25 (1968), S. 319-342 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A complex and parallel pattern of polymorphism for heterochromatic supernumerary segments in the M7 and S8 chromosomes has been found in 14 populations of the meadow grasshopperChorthippus parallelus. Nine distinct karyotype classes for these two chromosome pairs occur though they are not equally represented in different populations. Populations differ also with respect to the frequency of supernumerary segments they contain. In all populations the presence of supernumerary segments leads to a significant elevation of mean cell chiasma frequency compared to individuals from the same population lacking such segments. The extent of the effect appears to differ in different populations. The observed frequencies of S8 karyotypes conform to the expectations of a Hardy-Weinberg distribution. Those of the M7, however, do not, and in all but one of the 14 populations there is a significant excess of homokaryotypes. In the Ashurst population 26% of the individuals sampled were characterised by germ-line polysomy for the M4 chromosome, either in the form of entire tetrasomics or more usually as mosaics ranging from tri- to hepta-somics. In all these polysomics the M4 chromosomes in excess of two were regularly heteropycnotic at first meiotic prophase from zygotene to diakinesis. As a consequence of this multivalents are rare. Extra M4 chromosomes do not modify the chiasma characteristics of the other chromosomes in the complement. Nor do they modify the action of the supernumerary segments in any way.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01183124
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  • 8
    Electronic Resource
    Electronic Resource
    The B-chromosome system of myrmeleotettix maculatus (thunb.) (1967)
    Springer
    Chromosoma 21 (1967), S. 140-162 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract It is established that in populations of Myrmeleotettix maculatus with B-chromosomes these chromosomes occur at stable frequencies and are present to the same extent in both the males and the females of the same population. It is also established that the B-chromosome content of a population is positively correlated with its chiasma frequency and that, within a population, individuals with single B-chromosomes tend to have higher chiasma frequencies than individuals lacking B-chromosomes. Since this effect is not increased by the addition of further supernumeraries it is argued that selection operates in favour of individuals with single B-chromosomes. Finally it is shown that the level of B-chromosomes in a population is related to temperature and especially to rainfall so that B-chromosomes are absent from populations in climatically stringent environments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00343641
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  • 9
    Electronic Resource
    Electronic Resource
    An interchange which raises chiasma frequency (1967)
    Springer
    Chromosoma 21 (1967), S. 285-295 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In the grasshopper Cibolacris parviceps a chromosomal interchange is described which considerably raises the chiasma frequency in all the chromosomes, including the interchange itself. Both of the chromosomes involved in the interchange have pronounced heterochromatic regions and the possible role of heterochromatin in altering recombination is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00329552
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  • 10
    Electronic Resource
    Electronic Resource
    Parallel polymorphism for supernumerary segments in Chorthippus parallelus (Zetterstedt) (1969)
    Springer
    Chromosoma 28 (1969), S. 73-84 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Heterochromatic supernumerary segments, present in either or both the M7 and the S8 chromosomes of the Ashurst (AS) population of Chorthippus parallelus, lead to a significant elevation in mean cell chiasma frequency. This effect appears to be dosage independent within both the S8 and the M7 karyomorphs when these are considered separately. Neither is there any marked interaction between the two systems when they are combined with one another. The selective factors controlling the distribution of S8 karyomorphs within the population appear, however, to act quite independently of those which regulate the M7 karyomorph pattern. This is revealed in two ways. First, whereas the frequency of S8 karyomorphs conform to the expectations of a Hardy-Weinberg distribution those of the M7 do not. Secondly, though the pattern of distribution of S8 types is uniform throughout the AS population that of the M7 is not. This heterogeneity of M7 karyomorphs implies that the population is in some way internally stratified in terms of its breeding structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00325991
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