Enzyme polymorphism in plant populations

Brown, A. H. D.

doi:10.1016/0040-5809(79)90025-x

Cited by 578 publications

(338 citation statements)

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“…This result is only relatively unexpected as, in spite of the reported outbreeding habit of rye, outbreeding species often show a tendency to have lower heterozygosity than expected under panmixia (Brown, 1979); this phenomenon has been called the "heterozygosity paradox". Moreover, herbaceous outbreeders tend to show larger deficits than tree species (Brown, 1979).…”

Section: Discussionmentioning

confidence: 80%

Mating system in rye: variability in relation to the population and plant density

et al. 1989

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The amount of outcrossing was estimated using seven enzyme loci assayed in seven populations of rye (Secale cereale L.). Single-locus outcrossing values fluctuated widely from locus to locus in each population. The weighted mean single-locus estimates ranged from O•716 to 0946, and multilocus estimates ranged from O7O1 to 0910. The analysis showed that self-pollination occurred in the rye populations, and, as a result of selfing, populations contained homozygotes in excess of random mating expectations at the seedling stage of development. Low plant density, which causes low pollen density during fertilization, seems to weaken the self-incompatibility system; at low plant density, the outcrossing estimate was significantly lower than was obtained at high plant density.

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Section: Discussionmentioning

confidence: 80%

Mating system in rye: variability in relation to the population and plant density

et al. 1989

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“…The general prediction for predominantly outcrossing species is that populations should retain a high degree of genetic variability, and achieve extensive mixing of genes (Hamrick et al, 1979). However, Brown (1979) has noted an apparent 'paradox' between inbreeders and outcrossing species, with outcrossing species often exhibiting heterozygote deficiencies. Although a deficiency of heterozygotes has commonly been cited as evidence for inbreeding (see Linhart et al, 1981) (Nei, 1978) and geographic distance for five subpopulations of B. spinulosa.…”

Section: Discussionmentioning

confidence: 99%

“…Until recently, however, there have been relatively few studies on microgeographic differentiation of populations for which the mating system is known (Hamrick, 1982), and so these predictions have only rarely been tested for plant populations (but see; Ennos, 1985;Soltis & Soltis, 1988;Abbott & Gomes, 1989), Indeed, some of the species studied do not appear to conform to this general view. Spatial structuring of genotypes has been observed in some apparently outcrossing species (Linhart et at., 1981;Silander, 1984;Wendel & Parks, 1985), while inbreed- ing species sometimes show spatial genetic patterns more consistent with panmictic expectations (Brown, 1979). This can arise because the genetic structure of a population will also reflect factors not directly related to the mating system, including evolutionary history, the movement of genes through seed dispersal (e.g.…”

Section: Introductionmentioning

confidence: 99%

Population genetic structure of Banksia spinulosa

Carthew

1993

Heredity

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This study investigated the genetic structure of a population of the highly outcrossed perennial shrub, Banksia spinutosa. Three variable loci were detected; Pgm1, Adh1 and Pgi2. Some genetic differentiation was detected in the population, and as a whole it deviated from a panmictic unit.This primarily resulted from the behaviour of Pgi2. This locus exhibited a large deficit of heterozygotes, possibly in association with a Wahiund effect. However, deviations from panmixia were small compared with species which are predominantly self-fertilizing, and estimates of gene flow indicated that the movement of genes occurs over a fairly wide area. This study provides the first description of spatial genetic variability within a population of Banksia spinutosa.

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“…Comparative studies in several herbaceous families (e.g., Onagraceae, Oxalidaceae, Polemoniaceae, Gramineae) have provided evidence that the shift to selfing has evolved repeatedly in association with ecological radiation into temporary, pioneer habitats (Raven, 1979;Omduff, 1972;Grant and Grant, 1965;Stebbins, 1957). As the acquisition of autogamy is usually associated with a loss of outcrossing adaptations (Lloyd, 1965;Omduff, 1969) and reduction in the genetic variation of I Present address: Department of Biology, University of New Brunswick, Fredericton, New Brunswick E3B 6EI, Canada. populations (Brown, 1979;Hamrick et al, 1979), self-fertilization has been considered an evolutionary blind alley with selfing species rarely contributing to major evolutionary trends. Since the evolution of predominant selfing is usually viewed as unidirectional, it is often assumed that among closely related selfers and outcrossers, the former are derived (Lewis, 1954;Stebbins, 1957).…”

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confidence: 99%

VARIATION AND EVOLUTION OF BREEDING SYSTEMS IN THETURNERA ULMIFOLIAL. COMPLEX (TURNERACEAE)

1987

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Abstract. -The evolutionary and functional relationships among breeding systems and floral morphology were investigated in the Turnera ulmifolia complex. Predictions of a model of breeding system evolution among distylous and homostylous varieties were tested. Chromosome counts of 73 accessions revealed an association between breeding system and chromosome number. Diploid and tetraploid populations of five taxonomic varieties are distylous and self-incompatible, whereas hexaploid populations of three varieties are homostylous and self-compatible, The latter occur at different margins of the geographical range ofthe complex. Crossing studies and analyses of pollen and ovule fertility in F,'s revealed that the three homostylous varieties are intersterile.To test the prediction that,homostylous varieties are long homostyles that have originated by crossing over within the distyly supergene, a crossing program was undertaken among distylous and homostylous plants. Residual incompatibility was observed in styles and pollen of each homostylous variety with patterns consistent with predictions of the cross-over model. The intersterility of hexaploid varieties suggests that long homostyly has arisen on at least three occasions in the complex by recombination within the supergene controlling distyly. Deviation from expected compatibility behavior occurs in populations ofvar. angustifolia that have the longest styles. These phenotypes displayed the greatest separation between anthers and stigmas (herkogamy) and set little seed in crosses with long-or short-styled plants. This suggests that they are derived from long homostyles with shorter length styles. It is proposed that selection for increased outcrossing has favored the evolution of herkogamy in long homostyles.Estimates of outcrossing rate in a distylous population using allozyme markers confirmed that dimorphic incompatibility enforces complete outcrossing. Significant genetic variation for floral traits likely to influence the mating system, such as stigma-anther separation, occurs within and among homostylous populations ofvar. angustifolia on Jamaica. Estimates of the mating system of families from a population with varying degrees of stigma-anther separation, using five isozyme loci, were heterogeneous and ranged from t = 0.04-0.79. Families exhibiting the largest mean stigma-anther separation have higher outcrossing rates than those with little separation.

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Enzyme polymorphism in plant populations

Cited by 578 publications

References 102 publications

Mating system in rye: variability in relation to the population and plant density

Mating system in rye: variability in relation to the population and plant density

Population genetic structure of Banksia spinulosa

VARIATION AND EVOLUTION OF BREEDING SYSTEMS IN THETURNERA ULMIFOLIAL. COMPLEX (TURNERACEAE)

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