John W. Fondon

Molecular origins of rapid and continuous morphological evolution

Mutations in cis-regulatory sequences have been implicated as being the predominant source of variation in morphological evolution. We offer a hypothesis that gene-associated tandem repeat expansions and contractions are a major source of phenotypic variation in evolution. Here, we describe a comparative genomic study of repetitive elements in developmental genes of 92 breeds of dogs. We find evidence for selection for divergence at coding repeat loci in the form of both elevated purity and extensive length polymorphism among different breeds. Variations in the number of repeats in the coding regions of the Alx-4 (aristaless-like 4) and Runx-2 (runt-related transcription factor 2) genes were quantitatively associated with significant differences in limb and skull morphology. We identified similar repeat length variation in the coding repeats of Runx-2, Twist, and Dlx-2 in several other species. The high frequency and incremental effects of repeat length mutations provide molecular explanations for swift, yet topologically conservative morphological evolution.

Repeat Polymorphisms within Gene Regions: Phenotypic and Evolutionary Implications

We have developed an algorithm that predicted 11,265 potentially polymorphic tandem repeats within transcribed sequences. We estimate that 22% (2,207/9,717) of the annotated clusters within UniGene contain at least one potentially polymorphic locus. Our predictions were tested by allelotyping a panel of approximately 30 individuals for 5% of these regions, confirming polymorphism for more than half the loci tested. Our study indicates that tandem-repeat polymorphisms in genes are more common than is generally believed. Approximately 8% of these loci are within coding sequences and, if polymorphic, would result in frameshifts. Our catalogue of putative polymorphic repeats within transcribed sequences comprises a large set of potentially phenotypic or disease-causing loci. In addition, from the anomalous character of the repetitive sequences within unannotated clusters, we also conclude that the UniGene cluster count substantially overestimates the number of genes in the human genome. We hypothesize that polymorphisms in repeated sequences occur with some baseline distribution, on the basis of repeat homogeneity, size, and sequence composition, and that deviations from that distribution are indicative of the nature of selection pressure at that locus. We find evidence of selective maintenance of the ability of some genes to respond very rapidly, perhaps even on intragenerational timescales, to fluctuating selective pressures.

Having a BLAST with bioinformatics (and avoiding BLASTphemy)

Searching for similarities between biological sequences is the principal means by which bioinformatics contributes to our understanding of biology. Of the various informatics tools developed to accomplish this task, the most widely used is BLAST, the basic local alignment search tool. This article discusses the principles, workings, applications and potential pitfalls of BLAST, focusing on the implementation developed at the National Center for Biotechnology Information.

Detection of length-dependent effects of tandem repeat alleles by 3-D geometric decomposition of craniofacial variation

Topologically conservative morphological transformations typify the succession of species in the fossil record and also typify more subtle morphological variation within species. Isolation and quantification of morphological variation along its various intermingled modes becomes increasingly difficult as the structures under consideration increase in complexity. Here, we describe a comparative morphometric and genomic study in dogs in which complex three-dimensional craniofacial variation is mathematically distilled into simpler geometric components to test the hypothesis that incremental mutations at developmental loci result in simple geometric deformations of morphology. Combinations of candidate transforms are computationally evaluated for their ability to accurately transform a reference three-dimensional skull model into those of distinct breeds. A set of five simple basis functions are found to be sufficient to describe most craniofacial variation among dogs. Allele lengths of amino acid repeat length variants in developmental regulator genes, which frequently have quantitative effects on phenotype, were compared to geometric terms using Pearson correlation and regression. The coordinated quantitative representation of both phenotype and genotype improves the statistical power for the detection of causative genotype–phenotype relationships and enabled the characterization of the influence of Runx-2 coding repeat length on craniofacial variation among domestic dogs.

Bayesian statistical studies of the Ramachandran distribution

We describe a method for the generation of knowledge-based potentials and apply it to the observed torsional angles of known protein structures. The potential is derived using Bayesian reasoning, and is useful as a prior for further such reasoning in the presence of additional data. The potential takes the form of a probability density function, which is described by a small number of coefficients with the number of necessary coefficients determined by tests based on statistical significance and entropy. We demonstrate the methods in deriving one such potential corresponding to two dimensions, the Ramachandran plot. In contrast to traditional histogram-based methods, the function is continuous and differentiable. These properties allow us to use the function as a force term in the energy minimization of appropriately described structures. The method can easily be extended to other observable angles and higher dimensions, or to include sequence dependence and should find applications in structure determination and validation.

Low hanging fruit: a subset of human cSNPs is both highly non-uniform and predictable.

We present a point mutation classification method that contrasts SNP databases and has the potential to illuminate the relative mutational load of genes caused by codon bias. We group point variation gleaned from public databases by their wild-type and mutant codons, e.g. codon mutation classes (CMCs, 576 possible such as ACG-->ATG), whose frequencies in a database are assembled into a BLOSUM-style matrix describing the likelihood of observing all possible single base codon changes as tuned by the intertwined effects of mutation rate and selection. The rankings of the CMCs in any database are reshuffled according to the population stratification of the typical genotyping experiment producing that resources data. Analysis of four independent databases reveals that a considerable fraction of mutation in functional genes can be described by a few CMCs regardless of gene identity or population stratification in the genotyping experiment. For example, the top 5% (29/576) of CMCs account for 27.4% of the observed variants in dbSNP while the bottom 5% account for only 0.02%. For non-synonymous disease-causing mutation, 40.8% are described by the top 5% of all possible non-silent CMCs (22/438). Overall, the most observed polymorphism is a G-->A transition at CpG dinucleotides causing ACG, TCG, GCG, and CCG to frequently undergo silent mutation in any gene due to the putative lack of impact on the protein product. In order to assess how well CMC spectrums estimate the aggregate non-synonymous mutational trends of a single gene, a CMC matrix was applied to seven unrelated genes to compute the most likely point mutations. In excess of 87% of these mutation predictions are historically known to play an important role in a disease state according to published literature. CMC-based mutation prediction may aid design and execution of direct association genotyping studies.