oriented. The genome also contains insertion sequence (IS) elements, phage remnants, and many other patches of unusual composition indicating genome plasticity through horizontal transfer. Because of its extraordinary position as a preferred model in biochemical genetics, molecular biology

Abstract not found

Beans of the genus Phaseolus are considered a priority target for conservation because they are a valuable source of protein, vitamins, dietary fi ber, and minerals for farmers and consumers around the world, and especially in Mesoamerica where Phaseolus beans are an important component of the traditional milpa system of agriculture. In this cropping system, beans are interplanted with other staples, such as maize (Zea mays L.) and squash (Cucurbita spp.), and fi x atmospheric nitrogen, in addition to their role in human nutrition (Broughton et al., 2003). Together, beans and maize make up the foundation of the Mexican diet and food culture. In the southern Mexican state of Oaxaca, farmers regularly plant land-races of three species: common bean (P. vulgaris L.), runner bean (P. coccineus L.), and year bean (P. dumosus Macfad. [ = P. polyan-thus Greenm.]). Oaxaca falls within the Mesoamerican center of domestication and diversity for the genus Phaseolus, and the diver-sity of beans planted by the region’s farmers is among the highest

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A formula is given for the variance in the con-tribution to the total genome from the non-recurrent parent over successive generations in a backcrossing program. Results are illus-trated for mammals, including values for an approximate upper bound to the contribution. If individuals of a population (B) are crossed and then repeatedly backcrossed without selection to another population (A), the expected proportion of the auto-somal genotype of the crossbred popula-tion contributed by B halves each gener-ation. The actual contribution varies around this expectation, however, be-cause of Mendelian sampling. The mag-nitude of this variation is important in re-lation to the number of generations of upgrading of nonpedigree to purebred an-imals necessary before the upgraders should be accepted into a stud book (see Nicholas 1987). The related problems of the mean and variance of the length of chromosome segments about a marker maintained segregating with repeated backcrossing (Bartlett and Haldane 1935; Stam and Zeven 1981) and the variation in homozygosity in inbreeding systems (Franklin 1977; Stam 1980) have been an-alyzed. Simulation results for the variance in contribution with backcrossing, in the absence of selection, have been given by McClintock and Hammond (1981), but (to my knowledge) no general formulae for this variance have been published. Mod-ification of Franklin's (1977) results pro-vides a solution. Let n denote the generation of back-crossing, n = 1 being the first backcross. Let Z<#0 denote whether the fth autosomal locus inherited from the crossbred parent at generation n originates from the recur-rent population A (Z,(n) = 0) or B (Z/(n) = 1). Thus E(Z,Cn)) = '/2n. The probability that both loci / and / come from B is E(Z,Cn)ZXn)) = [(1- C(f)/2]» = [(1 + X«)/4]-, where c,y is the recombination fraction be-tween loci i and j and \0 = 1- 2cv. As the number (fc) of sites in the genome is very large, the variance of mean con-tribution, contains many more covariance than vari-ance terms, so terms in var(Z,(n)) can be ignored, and, hence, var(Zn) = Es[cov(Z,(n), Zm] = Es(Z,wZXn))- (1/4)", where Es denotes a mean over all pairs of sites. Assuming a continuous distribution of sites on a chromosome of length / with map positions xb Xj and corresponding re-combination parameters \(_xh x;),

Spatial and temporal genetic composition of Atlantic

Understanding how microbial genotypes are arrayed in space is crucial for identifying local factors that may influence the spatial distribution of genetic diversity. In this study we investigated variation in 16S rDNA se-quences and rep-PCR fingerprints of Streptomyces stains isolated from prairie

recurrent flash floods and debris flows causing massive mortalities. Using microsatellite data, a pattern of extreme genetic differentiation was found among populations (global FST of 0.716), which exceeds the highest values reported in freshwater fish. All locations showed low levels of genetic diversity

Abstract Landrace crops are formed by local adaptation, genetic drift and gene flow through seed exchange. In reverse, the study of genetic structure between landrace populations can reveal the effects of these forces over time.

When considering the genetic implications of immigrant gene flow, it is important to evaluate both the proportions of immigrant gametes and their genetic composition. We simultaneously investigated paternal and maternal gene flow in dispersed seeds in a natural population of Pinus densiflora