People of the Qatar peninsula represent a relatively recent founding by a small number of families from three tribes of the Arabian Peninsula, Persia, and Oman, with indications of African admixture. To assess the roles of both this founding effect and the customary first-cousin marriages among the ancestral Islamic populations in Qatar's population genetic structure, we obtained and genotyped with Affymetrix 500k SNP arrays DNA samples from 168 self-reported Qatari nationals sampled from Doha, Qatar. Principal components analysis was performed along with samples from the Human Genetic Diversity Project data set, revealing three clear clusters of genotypes whose proximity to other human population samples is consistent with Arabian origin, a more eastern or Persian origin, and individuals with African admixture. The extent of linkage disequilibrium (LD) is greater than that of African populations, and runs of homozygosity in some individuals reflect substantial consanguinity. However, the variance in runs of homozygosity is exceptionally high, and the degree of identity-by-descent sharing generally appears to be lower than expected for a population in which nearly half of marriages are between first cousins. Despite the fact that the SNPs of the Affymetrix 500k chip were ascertained with a bias toward SNPs common in Europeans, the data strongly support the notion that the Qatari population could provide a valuable resource for the mapping of genes associated with complex disorders and that tests of pairwise interactions are particularly empowered by populations with elevated LD like the Qatari.

A computer model has been developed to simulate the transmission characteristics of the B chromosomes in rye, and to provide a basis on which to identify, and to understand, the main factors responsible for determining the equilibrium B-frequency levels in open pollinating populations. The model has been devised by expressing the behaviour of the Bs, at various phases of the life cycle, in terms of mathematical equations. These equations contain parameters which determine the behaviour of the Bs at meiosis, pollen grain (and egg cell) mitosis and during the development of gametes and sporophytes.By exploring a range of values for the parameters it has been possible to ascertain that variation in the amount of meiotic elimination of Bs, as well as in their direction rate during nondisjunction in the pollen grain and egg cell, influence the final B-frequency equilibrium. Variation in the rate of nondisjunction on the other hand, affects the number of generations required to attain equilibrium more than the final equilibrium itself. Selection against gametes and plants containing Bs, even at levels which are higher than can reasonably be expected to occur naturally, cannot prevent the accumulation of Bs within populations, provided that high rates of directed nondisjunction are also occurring.The results are discussed in relation to the B chromosome polymorphism in natural populations of rye.

SUMMARYThe computer simulation model presented in the first paper in this series identified six parameters which were considered to represent the main processes determining the transmission rates and distribution characteristics of the B chromosomes of rye. Basically it was found that a drive mechanism is provided by the directed nondisjunction of Bs at first pollen grain, and first egg cell, mitosis and that the other parameters are largely concerned in modifying the drive and in regulating the final equilibrium B levels.The Bs were found to be "selfish" and to be capable of maintaining and dispersing themselves throughout populations even in the face of negative maladaptive effects upon reproductive and physiological fitness.In this paper estimates are presented, from published sources, of the real values of the parameters concerned. These estimates have been used to assess the application of the model and to determine the range and means of the parameters in relation to differing genetic and environmental influences.