Showing papers in "Heredity in 1984"
TL;DR: Sewall Wright's neighbourhood model indicates that the area containing a panmictic unit within a continuous and uniform array of organisms can be estimated by 4πσ2 where σ2 is the parent-offspring dispersal variance measured around a zero mean and relative to a single reference axis passing through the population.
Abstract: Sewall Wright's neighbourhood model indicates that the area containing a panmictic unit within a continuous and uniform array of organisms can be estimated by 4πσ2 where σ2 is the parent-offspring dispersal variance measured around a zero mean and relative to a single reference axis passing through the population. The method has proved popular in studies on higher plants but the literature is confused as to how the two components of dispersal variance, for pollen and seeds, should be combined. It is argued that σ2=½σp2+σs2 where σ2p and σ2s are pollen and seed dispersal variances already corrected to give axial variances. The consequences of using different methods are compared and some puzzling aspects of the previous literature are discussed.
163 citations
TL;DR: Data suggest that stocks either diverged rather recently or that the amount of gene flow between groups of fish classified as stocks has been large enough to prevent substantial differentiation, and that morphologic and ecologic divergence may to a large extent be environmentally induced.
Abstract: The Atlantic herring (Clupea harengus) stock complex is confusing from the perspectives of both evolutionary biology and systematics. There are numerous ecologically and morphologically divergent stocks classified as species, subspecies, races, tribes, etc. with an unknown degree of genetic differentiation and reproductive isolation between them. The genetic population structure of herring from the Scandinavian waters was analysed electrophoretically. The pattern for distribution of genetic variation was compared to that of the morphological characters most frequently used for stock classification, i.e., the number of vertebrae and keeled scales. Fish were collected from 17 locations distributed from the northern Gulf of Bothnia to the north-east Atlantic off the west coast of Norway. The genetic analysis was based on 17 electrophoretic loci, 13 of which were variable. There are statistically significant allele frequency heterogeneities, but there is a conspicuously small amount of genetic differentiation, even between stocks classified as representing different subspecies. More than 99 per cent of the total gene diversity was found within populations, and genetic distances are typically of the order of 0·001. The genotypic distribution of the total material is very similar to the one expected if all the samples had been drawn from a single panmictic population. There appears to be no association between the variation of morphological characters and that at electrophoretic loci, and this is true for the variation between as well as within samples. Data suggest that stocks either diverged rather recently or that the amount of gene flow between groups of fish classified as stocks has been large enough to prevent substantial differentiation, and that morphologic and ecologic divergence may to a large extent be environmentally induced.
156 citations
TL;DR: Diversity values, expressed as clones per individual, indicate that T. officinale proved to be more genotypically diverse than other clonal plants previously studied.
Abstract: Allozyme analysis, morphological characters, and histocompatibility relationships have revealed unexpected amounts of clonal diversity within and among populations of unisexual animals. Plant studies, likewise, have shown that genetic diversity exists in populations of plants that have restricted recombination. However, no work has been done which investigates the extent of genotypic diversity within and among populations of an obligate apomict. This study surveyed 22 North American populations of Taraxacum officinale, an obligate gametophytic apomict. Over 20 individuals from each population were assayed electrophoretically for three enzyme systems representing five different migration zones. Seed colour was used to determine seven phenological classes that, when combined with the allozyme morphs, resulted in 47 discernible clones among 518 individuals sampled. Chromosome analysis revealed the ploidy level to be triploid in all cases. The number of clones per population ranged from 1-13, with a mean of 5·0. Sixty-six per cent of the clones were restricted to single populations, and the mean number of populations containing a particular clone is 2·1. One widespread clone was found in all but three of the populations. Diversity values, expressed as clones per individual, indicate that T. officinale proved to be more genotypically diverse than other clonal plants previously studied. Spearman's Rank Correlation test failed to show a correlation of diversity with latitude or elevation.
102 citations
TL;DR: A unique euchromatic supernumerary segment was present in the five populations of Omocestus bolivari analysed, which appears negatively heteropyenotic during the first prophase of meiosis and does not C-band.
Abstract: C-Heterochromatin content of supernumerary chromosome segments of grasshoppers: Detection of an euchromatic extra segment
65 citations
TL;DR: Three closely related Drosophila species of the “obscura” group have been examined and some crosses are possible between them and F1 progeny were used in order to clarify chromosomal homologies.
Abstract: Three closely related Drosophila species of the “obscura” group have been examined: Dropophila madeirensis, D. guanche and D. subobscura. Some crosses are possible between them and F1 progeny were used in order to clarify chromosomal homologies. D. madeirensis has the following constitution in relation to D. subobscura: Am+1; JST; O3; U1+2 while D. guanche has: Am+g; Jg; Eg; O3+g; U1+2 (where m and g indicate inversions specific to those species). Some data are also presented on the inheritance of eight different quantitative characters used by some taxonomists to differentiate other palearctic obscura group species.
62 citations
TL;DR: It is concluded that reliable but conservative results are obtained by the proband method for heritabilities while analysis of variance techniques are more appropriate for estimating genetic correlations in low incidence, binomially distributed traits.
Abstract: Analysis of variance and proband methods for estimating heritabilities and genetic correlations in low incidence, binomially distributed traits are compared using a computer simulation. It is concluded that reliable but conservative results are obtained by the proband method for heritabilities while analysis of variance techniques are more appropriate for estimating genetic correlations. These results apply providing that the incidences involved are not much less than 0·01, and that the true genetic correlation is not very small. These methods are then applied to pedigree broiler data, including information on live-weight and various skeletal defects. It appears that all the defects considered are heritable, that leg problems have positive genetic correlations with weight, and that it is reasonable to group abnormalities together for the purposes of selection.
61 citations
TL;DR: The Drosophila melanogaster × D. simulans hybrids system illustrates the potential importance of regulatory genes in evolution and provides a model for investigating the molecular basis of evolved regulatory differences.
Abstract: In Drosophila melanogaster X D. simulans hybrids, the alcohol dehydrogenase (ADH) electromorphs characteristic of the two parents display tissue- and stage-specific differences in relative level of expression. This implies distinct cis-acting regulatory elements associated with the respective Adh alleles. These cis-acting elements account in part, but not completely, for markedly different overall patterns of ADH expression in the two species. The regulatory patterns seem to be adaptively significant since they correlate with species-specific patterns of ethanol tolerance. The activity differences are accounted for by different levels of enzyme protein, but the underlying mechanisms have not been fully analysed and may be complex. Independent evolution of various aspects of the ADH developmental programme may relate to use of different promoters for transcription of the Adh locus in different developmental contexts. This system illustrates the potential importance of regulatory genes in evolution and provides a model for investigating the molecular basis of evolved regulatory differences.
60 citations
TL;DR: A survey of outcrossing rates at the ray floret locus in an Edinburgh population of Senecio vulgaris in 1979 and 1980 showed that in both years radiate plants outcrossed at much greater frequencies than non-radiate plants.
Abstract: Polymorphism for outcrossing frequency at the ray floret locus in Senecio vulgaris L. II. Confirmation
58 citations
TL;DR: ESS models support the prediction of Westoby and Rice (1982) and Queller (1983), based on relatedness arguments, that genes affecting the amount of parental resources to be invested in seeds will be selected towards different outcomes, depending on the tissue in which they are expressed.
Abstract: ESS models support the prediction of Westoby and Rice (1982) and Queller (1983), based on relatedness arguments, that genes affecting the amount of parental resources to be invested in seeds will be selected towards different outcomes, depending on the tissue in which they are expressed. In order of decreasing “preference” for investment in their own seed, the tissues generally rank as: embryo, endosperm, gametophyte, maternal plant. A more detailed model reveals that whether or not selection will favour an endosperm allele for taking more investment depends on frequency and dosage. These effects are analogous to those arising from inbreeding in other kin selection models, and they disappear when a covariance form of the relatedness coefficient is used.
58 citations
TL;DR: In this article, seven varieties of Pisum sativum from Afghanistan, Iran, Tibet and Turkey were tested for nodulation by 25 diverse strains of Rhizobium leguminosarum.
Abstract: Seven varieties of Pisum sativum from Afghanistan, Iran, Tibet and Turkey were tested for nodulation by 25 diverse strains of Rhizobium leguminosarum. The pea varieties were resistant to nodulation by 13 rhizobial strains from temperate regions, and formed few or no nodules. The varieties nodulated with 4 of 12 rhizobial strains from Middle Eastern soils. The plant-rhizobia specificity was identical to Pisum sativum var. “Afghanistan”. Crosses were made among five nodulation resistant varieties and “Afghanistan”. Genetic analysis indicates that the strain specific nodulation resistance in each of the five pea varieties is allelic with the sym-2 gene in “Afghanistan”. Surveys of worldwide pea collections have failed to discover varieties which are never nodulated by any rhizobial strain. There appears, however, to be a class of nodulation resistant peas from the Middle East which have the same restricted strain specificity.
52 citations
TL;DR: The data give strong support for Lusis's (1961) suggestion that increases in melanic frequency observed during the summer in Berlin (and in the Netherlands) can be explained by more frequent mating of melanics as a result of the effects of thermal melanism.
Abstract: Selection along clines in the ladybird adalia bipunctata in the netherlands: A general mating advantage to melanics and its consequences
TL;DR: The high proportion of non-zero y values in all fungi, with large departures from zero being most extreme in Ascobolus and Sordaria brevicollis, shows that gene conversion could often be an important force in changing allele frequencies in favour of mutant or wild-type in these organisms.
Abstract: In order to determine how important gene conversion is as a force in populations, extensive surveys have been made to determine the limits, distributions and typical values of evolution-related conversion parameters from various fungi, Drosophila and maize. The conversion frequency, c, had an enormous range for different mutations within a species, with loci often having different means and limits for c. b, the frequency of a particular allelle in the products of meiotic tetrads or octads with aberrant segregation ratios, often showed values near the theoretical extremes; d, disparity in direction of conversion, was frequent and often extreme, b and d could only be studied in fungi, and their less extreme values in Saccharomyces than in Sordaria or Ascobolus are clearly related to the lack of frame-shift mutations in the yeast data. For different mutations at a locus, neither c nor b showed normal distributions; both gave dispersed distributions, sometimes multi-modal for b ; c and b were not usually correlated. y, the force of meiotic gene conversion on allele frequencies, had a large range of positive and negative values, with different loci often having quite different limits and mean absolute values. For different mutations at a locus, y showed dispersed distributions, with little tendency to cluster around zero. The high proportion of non-zero y values in all fungi where this could be studied, with large departures from zero being most extreme in Ascobolus and Sordaria brevicollis, shows that gene conversion could often be an important force in changing allele frequencies in favour of mutant or wild-type in these organisms. Even in organisms with much lower c or absolute d values, conversion could still be important, depending on dominance, selection coefficients and mutation rates. Presumed frame-shifts tended to have more extreme disparity and hence higher absolute y values than did presumed base-substitutions, but with no consistent c differences. Induced mutations had similar or slightly higher absolute y values compared with spontaneous mutations.
TL;DR: Data from F2 and doubled monoploid populations segregating for major gene markers indicated that the dwarfing gene present in the spring barley varieties Golden Promise and Midas was located on chromosome 7.
Abstract: The chromosomal location of the dwarfing gene present in the spring barley variety golden promise
TL;DR: It is argued that while the differences between male steriles and hermaphrodites in sexual reproduction contribute to the maintenance of gynodioecy, they probably do not explain it fully and should be interpreted as pleiotropic effects of the male sterility genes.
Abstract: Gynodioecy in Plantago lanceolata L. III. Sexual reproduction and the maintenance of male steriles 1
TL;DR: An attempt has been made to devise two new estimators of the number of S-alleles in a population which do not assume that their frequencies are equal, and these are investigated with data from eight populations generated on the computer in which the numbers and frequencies of alleles are known.
Abstract: Three methods of estimating the number of S-alleles in a population have been proposed in the literature (Bateman, 1947; Whitehouse, 1949; Paxman, 1963). These methods, all of which assume that genotype frequencies in the population are equal, are described briefly and are used to estimate the number of alleles in populations of Trifolium pratense (Williams and Williams, 1947), Oenothera organensis (Emerson, 1939) and Papaver rhoeas (Campbell and Lawrence, 1981b; Lawrence and O'Donnell, 1981). The estimates yielded by Bateman's and White-house's methods are similar to those given by Paxman's maximum likelihood method with the Trifolium and Oenothera data where there is little reason to suppose that the allele frequencies are other than equal. Bateman's method, however, breaks down when used on the Papaver data in which the S-allele frequencies are known to be unequal; and Whitehouse's and the maximum likelihood methods yield estimates which are biased downwards when used on these data. An attempt has been made, therefore, to devise two new estimators of the number of S-alleles in a population which do not assume that their frequencies are equal. The properties of these estimators has been investigated with data from eight populations generated on the computer in which the numbers and frequencies of alleles are known. One of these new estimators (E2) yields estimates which are less biased downwards than those given by Paxman's method when allele frequencies are unequal, but gives estimates which are biased upwards when these frequencies are equal. The other estimator (E1) is generally less satisfactory than the first, particularly when the number of alleles in the population is large. Though neither of these new estimators are wholly satisfactory, there is some justification for using E2 when allele frequencies are known to be unequal. Estimates given by E2 when used on the Papaver data range from 34 to 42 alleles which, bearing in mind that these estimates are still likely to be biased downwards, suggests that the number of alleles in natural populations of this species is likely to be between 40 and 45. A new procedure for calculating confidence intervals for maximum likelihood estimates, assuming equal allele frequencies, is also described and applied to the Oenothera and Papaver data.
TL;DR: This species can be hybridised by somatic cell fusion with wild type species lacking selectable markers by developing a double mutant with a negative (auxotrophic) and a positive (resistance) selection marker in a species of interest.
Abstract: Leaf mesophyll protoplasts of a nitrate reductase deficient, streptomycin resistant double mutant of Nicotiana tabacum were fused with cell suspension protoplasts of wild type N. rustica. Hybrid colonies were selected for nitrate reductase proficiency and streptomycin resistance. Green, actively proliferating colonies were recovered in the selection medium. Eleven of twenty green colonies, transferred to regeneration medium, produced plants. Regenerated plants were analysed for their vegetative and floral characteristics, Fraction 1 protein polypeptide composition and leaf esterases. All the eleven regenerants were nuclear somatic hybrids possessing the chloroplast of the N. tabacum parent. By developing a double mutant with a negative (auxotrophic) and a positive (resistance) selection marker in a species of interest, this species can be hybridised by somatic cell fusion with wild type species lacking selectable markers.
TL;DR: Although the selection affecting Adh did not generally differ among the four selection environments, it differed highly significantly among the eight base populations, and the only aspect of the coefficients which was consistent across base populations was FS heterozygote superiority.
Abstract: Eight freshly caught Australasian mass collections ranging in Adh F frequency from 4 to 96 per cent were each divided into eight selection lines. Two selection lines from each base population were put on one of four types of medium-standard food supplemented with 0 per cent, 3 per cent, 6 per cent or 9 per cent ethanol. After 30 generations the tolerance of 6 per cent and 9 per cent selection lines on a test dose of 9 per cent ethanol was greater than that of the 0 per cent lines on this dose. The tolerance of the 3 per cent lines on this dose was less than that of the 0 per cent lines. There were no significant differences in the tolerance responses across the eight base populations but in only one did Adh frequencies diverge among the four ethanol selection environments: F frequencies in the Brisbane 9 per cent lines were higher than in the Brisbane 0 per cent, 3 per cent and 6 per cent lines. Although the selection affecting Adh did not generally differ among the four selection environments, it differed highly significantly among the eight base populations. The equilibrium F frequencies predicted from the maximum likelihood estimates of the selection coefficients were in close agreement with the frequencies observed in the original collections. The only aspect of the coefficients which was consistent across base populations was FS heterozygote superiority.
TL;DR: There appears to be an advantage to those individuals of this perennial species that possess maximal allelic diversity at this locus, especially in transitional climatic areas where variations in temperature and water availability are particularly high and unpredictable, as only tetraploid plants with the highest allelic Diversity are found in such fluctuating conditions.
Abstract: The role of polyploidy in the adaptive significance of polymorphism at the GOT 1 locus in the Dactylis glomerata complex
TL;DR: Nine palearctic and one North American Drosophila species of the obscura group have been compared with respect to electrophoretically detectable differences at 24 enzyme loci to calculate the genetic distances between the species.
Abstract: Evolution of the obscura group drosophila species. II. Phylogeny of ten species based on electrophoretic data
TL;DR: Nucleolar activity and competition (amphiplasty) has been analysed in diploid, tetraploid and hexaploid species of Aegilops using a highly reproducible silver-staining procedure to analyse the activity of the nucleolar organiser regions (NORs).
Abstract: Nucleolar activity and competition (amphiplasty) has been analysed in diploid, tetraploid and hexaploid species of Aegilops using a highly reproducible silver-staining procedure. A comparative analysis of somatic metaphase chromosomes by phase contrast, C-banding and Ag-staining was made to analyse the activity of the nucleolar organiser regions (NORs). With the exception of Ae. crassa 4x, amphiplasty occurs in all the tetraploid and hexaploid species analysed. The U genome from Ae. umbellulata suppresses completely the NOR activity of the genomes M° (Ae. ovata), Sv (Ae. variabilis), D (Ae. juvenalis) and C (Ae. triuncialis) and that of one pair of the nucleolar organiser chromosomes of the genomes Mc (Ae. columnaris), Mb (Ae. biuncialis), Mj (Ae. juvenalis) and Mt (Ae. triaristata 6×). The nucleolar activity of the D genome is completely suppressed by the genomes U (Ae. umbellulata), C (Ae. cylindrica) and Mv (Ae. ventricosa).
TL;DR: The seaweed fly, Coelopa frigida, is polymorphic for two gene arrangements on chromosome I, and the egg to adult viability of heterokaryotypes is higher than either homokaryotype.
Abstract: The seaweed fly, Coelopa frigida, is polymorphic for two gene arrangements on chromosome I. Inversion frequencies in natural populations are very stable, both geographically and temporally and there is a consistent excess of heterokary-otypes. Laboratory experiments are reported which demonstrate that the egg to adult viability of heterokaryotypes is higher than either homokaryotype. This advantage increases markedly with larval density. Field samples also show a strong correlation between larval density and relative viability, expressed as the excess of heterokaryotypes over Hardy-Weinberg expectations. Larvae of a closely related species, C. pilipes contribute significantly to this density effect in natural populations.
TL;DR: Isoenzyme variation in six species of Australian reptile ticks is used to examine a hypothesis that populations of parasites will diverge more rapidly from each other than populations of non-parasites, and supports Price's prediction that parasite populations have low levels of genetic variability.
Abstract: In this paper isoenzyme variation in six species of Australian reptile ticks is used to examine a hypothesis, proposed by Price (1977), that populations of parasites will diverge more rapidly from each other than populations of non-parasites. The data support Price's prediction that parasite populations have low levels of genetic variability. The average heterozygosity per locus was less than 2·5 per cent in each reptile tick species, compared with a mean value of 11·23 per cent for 93 non-parasitic invertebrates (Nevo 1978). Price also predicted large genetic variation between parasite populations, but this was not normally the case within reptile tick species. Where genetic distance was large between populations it could be explained by processes which were not unique to parasites.
TL;DR: Combining the data on density and dispersal with an estimate of variance of family size, yields estimates of effective neighbourhood size ranging from 115 to 4130, which suggest that T. pisana is rather sedentary when compared with the few other snail species for which comparable information is available.
Abstract: Studies of population structure were undertaken at six sites in the Tenby (South Wales) colony of the Mediterranean coastal land snail Theba pisana (Muller). Over four years, the density of adult (two-year-old) snails was estimated as ranging from 39 to 202 m−2 during the summer active season; half-grown juvenile (one-year-old) density was estimated during the same time of year as between 13 and 436 m−2; no estimates were made of the density of younger snails. Significant aggregation was shown for both adults and juveniles. Estimates of variance of dispersal over 100 days (0·489 to 1·601 m2) suggest that T. pisana is rather sedentary when compared with the few other snail species for which comparable information is available. Combining the data on density and dispersal with an estimate of variance of family size, yields estimates of effective neighbourhood size ranging from 115 to 4130. These results are compared with data for other organisms, especially other species of land snail.
TL;DR: The behaviour of Drosophila melanogaster populations originating from three different fruit types in the same orchard was compared in a wind tunnel olfactometer and found that after two generations of laboratory culture, flies tended to be attracted to the odours of the fruit type from which they originated.
Abstract: The behaviour of Drosophila melanogaster populations originating from three different fruit types (plums, peaches, apples) in the same orchard was compared in a wind tunnel olfactometer. After two generations of laboratory culture, flies tended to be attracted to the odours of the fruit type from which they originated. Thus, genetic variation for olfactory response affects habitats selected, and hence the microdistribution of D. melanogaster in the field.
TL;DR: The present experiments report the results of a similar procedure where females of the laboratory strain have been used as the recurrent backcross parent, in this case recombination between the field and laboratory genomes is precluded during backcrossing.
Abstract: Previous results demonstrated that modification of the genetic background produced changes in the fitness of genotypes at the diazinon resistance locus in Lucilia cuprina (McKenzie et al., 1982). Fitness sets were estimated from population cage studies following disruption of the field genome by generations of backcrossing of a resistant field strain to males of a susceptible laboratory strain. The present experiments report the results of a similar procedure where females of the laboratory strain have been used as the recurrent backcross parent. In this case recombination between the field and laboratory genomes is precluded during backcrossing. Population cage results were analogous to those of the previous experiments suggesting fitness modifiers were unlinked to the diazinon resistance locus on chromosome IV. The use of chromosome substitution lines provided confirmation. Major fitness modifiers were mapped to chromosome III. The relevance of changes in the fitness sets of insecticide resistance genotypes, because of genetic background modification, to models of the evolution of insecticide resistance is discussed.
TL;DR: Frequency-independent selective differences between colour forms broaden the possibilities for aposematic polymorphism but lead to monomorphism if too large, which may explain polymorphism for warning colouration in a number of jumping or moderately unpalatable insects.
Abstract: Selection for warning colouration in well-defended species should lead to a single colour form in each local population, but some species are locally polymorphic for aposematic colour forms. Single-locus two-allele models of frequency-dependent selection indicate that combined apostatic and aposematic selection may maintain stable polymorphism for one, two or three aposematic forms, provided that at least one form is subject to net apostatic selection. Frequency-independent selective differences between colour forms broaden the possibilities for aposematic polymorphism but lead to monomorphism if too large. Concurrent apostatic and aposematic selection may explain polymorphism for warning colouration in a number of jumping or moderately unpalatable insects.
TL;DR: Crosses among American, English, and Italian stocks demonstrate that populations of C. nemoralis are reproductively compatible on a continental scale, and the decoupling of genetic divergence from speciation emphasizes the limitations of viewing the process of speciation solely in genetic terms.
Abstract: Cepaea nemoralis is remarkable for its geographic variation for both shell polymorphism and allozymes. An electrophoretic study of 20 loci revealed genetic identities as low as 0.53 between English and Italian populations. Despite this genetic divergence, crosses among American, English, and Italian stocks demonstrate that populations of C. nemoralis are reproductively compatible on a continental scale. This reproductive compatibility in the face of large-scale genetic divergence indicates the danger of using a genetic index to assess reproductive relationships. The decoupling of genetic divergence from speciation emphasizes the limitations of viewing the process of speciation solely in genetic terms. A comparison of Cepaea with another genus of land snails, Partula, suggests that competition may be an important determinant of the likelihood of speciation. C. nemoralis from Lexington, Virginia, were included in the matings and electrophoretic comparisons, in order to test conflicting proposals on the origin of that population. Both sets of data favour a British, rather than an Italian, origin, but are also compatible with earlier evidence that the Lexington population is of hybrid origin.
TL;DR: In a field study of the B locus polymorphism in Ghana, significant changes in the morph frequencies were recorded over eighteen months at Cape Coast, and the hypothesis that polymorphism arose as a result of the overlapping of previously isolated geographical races was discussed.
Abstract: The polymorphism of Danaus chrysippus is anomalous since it is a distasteful butterfly. In a field study of the B locus polymorphism in Ghana, significant changes in the morph frequencies were recorded over eighteen months at Cape Coast. There were also significant differences between localities. There was some evidence that brown morphs are favoured by wet conditions, and that orange forms have higher survival rates as caterpillars. There were no differences between forms in larval foodplants, sex ratio, body size, wing damage, mating success, or in the effects of weather on adult activity. There was however, strong assortative mating between forms. Crosses with Kenyan females gave aberrant segregations for the sex chromosomes and the C locus. The results are discussed with regard to the hypothesis that polymorphism arose as a result of the overlapping of previously isolated geographical races.
TL;DR: Electrophoretic analyses of genetically controlled enzyme polymorphisms were carried out on broods of diploid gynogenetic rainbow trout alevins, showing that diploidsisation was caused by the retention of the second polar body and also demonstrated complex cross-over phenomena.
Abstract: Electrophoretic analyses of genetically controlled enzyme polymorphisms were carried out on broods of diploid gynogenetic rainbow trout alevins, produced by heat-shocking eggs which had been fertilised with u.v.-irradiated sperm. The results showed that diploidisation was caused by the retention of the second polar body and also demonstrated complex cross-over phenomena.
TL;DR: Genetic isolation and microhabitat differences are suggested causes of this high degree of genetic differentiation, and possible incipient speciation of Collinsia verna in the mid-west United States.
Abstract: Intraspecific variation in nuclear DNA content in Collinsia verna nutt. (Scrophulariaceae)