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DNA fingerprint is a pattern of a variable number of bands (DNA fragments) with different sizes on a Southern gel for each individual, generated by one or many VNTR loci. Genetic divergence between individuals within and between populations can be studied in terms of number of shared bands between individuals. Using a population genetic model we show that the expectations of measures of genetic distance between populations based on band sharing data from DNA fingerprint patterns are functions of composite parameters M = 4Nv, and time of divergence (t) between populations, where N is the effective size of the populations, and ν, the mutation rate. The expected genetic distance remains linear with time of divergence at least up to N generations as long as the average heterozygosity at the DNA fingerprint loci remains at or below 90%. Neither incomplete knowledge of the allele frequencies at each locus, nor the unknown number of loci underlying DNA fingerprint pattern, compromise these evolutionary dynamics of DNA fingerprint patterns. Applications of this theory to data on three human populations, and review of literature indicate that co-migration of alleles, and the presence of syntenic loci underlying the fingerprint pattern have little impact of the reliability of evolutionary conclusions from DNA fingerprint studies.
The interpulse interval (IPI) of courtship song in the Drosophila auraria complex is the only parameter that is consistently species-specific among the several courtship elements examined within the complex. The genetic basis of the species-specific courtship song was examined by analysing the song of interspecific hybrids and of backcross progeny. IPI of all interspecific hybrids except two showed intermediate values, suggesting autosomal control of species-specific IPI. However, significant deviation for shorter IPI from midparent was found in thirteen out of 20 crosses. The chromosomal analysis between D. auraria and D. biauraria revealed that the two major autosomes had significantly large effects on IPI, but the sex chromosome and cytoplasm had no effect. Since no interaction was detected, it is concluded that each autosome acts additively in the determination of species-specific IPI. The common ancestors of the D. auraria complex may also have had autosomal control of IPI, which has been conserved during speciation in the complex.
The singedvery weak mutation was created by the sequential addition of two P transposable elements to the singed gene. The mutation can be somatically unstable through the action of a dominant maternal effect mutation on the second chromosome. It is also unstable in the germ line in these conditions. Sequencing of the region of the P insertions in the mutation reveals that the two inserted elements have single internal deletions, and the larger of the two is a copy of the KP element. The mutation will generate, at high frequencies, strongly singed and pseudo-wild type products by reversions occurred in the germline. These are the result of the precise excision of the smaller and the larger elements respectively. By PCR amplification of dissected thoraces we show that the somatic instability of the mutation, from a weak to a strong singed phenotype, is also caused by the excision of the smaller of the two elements.
Patterns of P element establishment and evolution were compared in populations of D. melanogaster and D. simulans. For each species, mixed populations were initiated with M strain flies lacking P elements together with P strain flies having similar P element copy numbers and phenotypes. The mixed populations were subsequently maintained under similar environmental conditions. On the basis of gonadal sterility assays, P elements tended to be significantly more active in D. melanogaster than in D. simulans populations. This activity difference between the two species was positively associated with P element copy number, determined by restriction enzyme analysis, and transposition frequency, as determined by a transposition assay. Host factors are the most likely explanation for the observed species variation. Difficulty of establishment may be a factor determining the absence of P elements in natural populations of D. simulans.
A computer model is developed that simulates Marker Assisted Selection (MAS) in a population produced by a cross between two inbred lines. Selection is based on an index that incorporates both phenotypic and molecular information. Molecular markers contributing to the index and their relative weights are determined by multiple regression of individual phenotype on the markers. The model is applied to investigate the efficiency of MAS as affected by several factors including total number of markers in the genome, number of markers contributing to the index, population size and heritability of the character. It is demonstrated that selection based on genetic markers can effectively utilize the linkage disequilibrium between genetic markers and QTLs created by crossing inbred lines. Selection is more efficient if markers contributing to the index are re-evaluated each generation than if they are evaluated only once. Increasing the total number of markers in the genome as well as the number of markers contributing to the index does not necessarily result in a higher efficiency of selection. Moreover, too many markers may result in a weaker response to selection. Population size is shown to be the most important factor affecting the efficiency of MAS.
Maximum likelihood estimation methods with an individual animal model were used to analyse a bi-directional selection experiment, with control, for cannon bone length in Scottish Blackface sheep. A method is described for partitioning the likelihood to allow within- and between-line estimates of genetic variance. It is concluded that both sources of information made substantial contributions to the precision of the base population heritability estimate. The implications for different experimental designs and varying heritability are discussed.
We have investigated the interchromosomal effect of the naturally-occurring paracentric inversions In(2L)t and In(3R)P on meiotic recombination in two regions of the X chromosome in Drosophila melanogaster. Previous authors have suggested that the rate of recombination at the tip of the X chromosome may be substantially higher in some natural populations than values measured in the laboratory, due to the interchromosomal effect of heterozygous autosomal inversions. This suggestion was motivated by observations that transposable elements are not as common at the tip of the X chromosome as predicted by recent research relating reduced meiotic exchange to increased element abundance in D. melanogaster. We examined the effects of heterozygous In(2L)t and In(3R)P on recombination at both the tip and base of the X chromosome on a background of isogenic major chromosomes from a natural population. Both inversions substantially increased the rate of recombination at the base; neither one affected recombination at the tip. The results suggest that the presence of inversions in the study population does not elevate rates of crossing over at the tip of the X chromosome. The relevance of these results to ideas relating transposable element abundance to recombination rates is discussed.
We study multi-locus models for the accumulation of disadvantagenous mutant alleles in diploid populations. The theory used is closely related to the quasi-species theory of molecular evolution. The stationary mutant distribution may either be localized close to a peak in the fitness landscape or delocalized throughout sequence space. In some cases there is a sharp transition between these two cases known as an error threshold. We study a multiplicative fitness landscape where the fitness of an individual with j homozygous mutant loci and k heterozygous loci is wjk = (1 − s)j (1 − hs)k. For a sexual population in this landscape there are two types of solution separated by an error threshold. For a parthenogenetic population there may be three types of solution and two error thresholds for some values of h. For a population reproducing by selfing the solution is independent of h, since the frequency of heterozygous individuals is negligible. The mean fitnesses of the populations depend on the reproductive method even for the multiplicative landscape. The sexual may have a higher or lower fitness than the parthenogen, depending on the values of h and u/s. Selfing leads to a higher mean fitness than either sexual reproduction or parthenogenesis. We also study a fitness landscape with epistatic interactions with wjk = exp(− s(2j + k)α). The sexual population has a higher fitness than the parthenogen when α > 1. This confirms previous theories that sexual reproduction is advantageous in cases of synergistic epistasis. The mean fitness of a selfing population was found to be higher than both the sexual and the parthenogen over the range of parameter values studied. We discuss these results in relation to the theory of the evolution of sex. The fitness of the stationary distribution in cases where unfavourable mutations accumulation is one factor which could explain the observed prevalence of sexual reproduction in natural populations, although other factors may be more important in many cases.