Number of incompatibility alleles in clover and other species

Abstract

Atwood's (1942, 1944) data on Tnfolium repens, those of Williams & Williams (1947) on T pratense and those of Williams (1951) on T hybridum have been re-analysed to provide maximum likelihood estimates of the number of incompatibility alleles in the populations or breeders' stocks from which the samples investigated were obtained. These new estimates suggest that populations of T repens contain about 100 alleles and those of T pratense contain up to twice this number. The single estimate from T hybridum, however, suggests that the species in North America possesses only 17 S-alleles. The estimates from clover populations are compared with those from the nine most thoroughly investigated species of other selfincompatible flowering plants and confirm the long-held belief that populations of T repens and T pratense contain more S-alleles than those of the latter. It is argued that the most likely explanation of the large number of S-alleles that natural populations of these species appear to contain is that they are substructured into a large number of semi-isolated neighbourhoods.

The population genetics of sporophytic self-incompatibility in Senecio squalidus L. (Asteraceae) I: S allele diversity in a natural population

“…These modified estimators are presented below as equations 3 and 4 (corresponding to modified versions of equations 1 and 2, respectively). Equation 4 was originally derived from equation 2 by Lawrence (1996) to estimate population S allele number for the two locus GSI system found in the Poaceae, but may also be applied to the problem of estimating population S allele number for SSI systems. Equation 3 was derived from equation 1 using similar principles to those used by Lawrence (1996) to modify the Paxman (1963) estimator, namely that m, the number of S alleles sampled becomes, r, the number of plants sampled (m = r).…”

“…Equation 4 was originally derived from equation 2 by Lawrence (1996) to estimate population S allele number for the two locus GSI system found in the Poaceae, but may also be applied to the problem of estimating population S allele number for SSI systems. Equation 3 was derived from equation 1 using similar principles to those used by Lawrence (1996) to modify the Paxman (1963) estimator, namely that m, the number of S alleles sampled becomes, r, the number of plants sampled (m = r). Similarly, the error range for the modified Paxman (1963) estimator (equation 4) can be derived from the error range for the original estimator (equation 2) presented in Paxman (1963).…”

“…The performance of the modified Paxman (1963) estimator relative to its unmodified counterpart was tested using Monte Carlo simulations of published diploid S genotype datasets and associated population S allele number estimates for natural SSI populations of other species (Stevens and Kay, 1989;Kowyama et al, 1994), where the modified estimator was calculated from 1000 resampled haploid datasets consisting of single randomly chosen S alleles. (Lawrence, 1996) Measuring the thoroughness of the SI study Repeatability (R) is a standard measure of the thoroughness with which an S allele assay has been carried out and was calculated according to equation 5. The resulting value is a proportion ranging from zero (as many different S alleles identified as S alleles sampled) to one (the minimum number of S alleles possible for a SSI system (ie, 2) identified in the entire sample).…”

Incompatibility in angiosperms

“…Numbers, frequencies and distribution of SI alleles Lawrence (1996) analyzed earlier data from Atwood et al (1942Atwood et al ( , 1944; Williams and Williams (1947) and Williams (1951) on the number of S-alleles in Trifolium to evaluate the number of alleles in the populations studied. Lawrence (1996) compared the re-visited estimates to those available from nine other species of flowering plants with homomorphic SI.…”

Consequences of Population Structure on Genes Under Balancing Selection

“…Although population subdivision has been invoked occasionally as an intuitive explanation for observed patterns of polymorphism (Lawrence 1996), little theoretical attention has been paid to clarifying the effects of population subdivision on genes under balancing selection. Wright (1939) developed an analytic model to treat the case of gametophytic self-incompatibility (GSI) in a subdivided plant population.…”