Shotgun haplotyping: a novel method for surveying allelic sequence variation

Decoding Genetic Variations: Communications-Inspired Haplotype Assembly

High-throughput DNA sequencing technologies allow fast and affordable sequencing of individual genomes and thus enable unprecedented studies of genetic variations. Information about variations in the genome of an individual is provided by haplotypes, ordered collections of single nucleotide polymorphisms. Knowledge of haplotypes is instrumental in finding genes associated with diseases, drug development, and evolutionary studies. Haplotype assembly from high-throughput sequencing data is challenging due to errors and limited lengths of sequencing reads. The key observation made in this paper is that the minimum error-correction formulation of the haplotype assembly problem is identical to the task of deciphering a coded message received over a noisy channel-a classical problem in the mature field of communication theory. Exploiting this connection, we develop novel haplotype assembly schemes that rely on the bit-flipping and belief propagation algorithms often used in communication systems. The latter algorithm is then adapted to the haplotype assembly of polyploids. We demonstrate on both simulated and experimental data that the proposed algorithms compare favorably with state-of-the-art haplotype assembly methods in terms of accuracy, while being scalable and computationally efficient.

Direct haplotyping of bi-allelic SNPs using ARMS and RFLP analysis techniques

Haplotype analysis of single nucleotide polymorphisms (SNPs) is an important and rapidly growing approach for association studies. In recent years, statistical procedures to haplotype determination from genotypic information have employed in population studies. These procedures, even though some advantages for estimation of haplotype frequencies in large population samples, have limitations in the accuracy of the analysis. In this study, we have designed a reliable method for direct haplotyping of polymorphic sites using the amplification refractory mutation system (ARMS) and restriction fragment length polymorphism (RFLP) analysis techniques. We applied the method to determination of haplotypes composed of three SNPs within the paraoxonase1 gene promoter and found the approach can be used in many studies in population and in a variety of clinical settings.

A chromosomal rearrangement hotspot can be identified from population genetic variation and is coincident with a hotspot for allelic recombination

Insights into the origins of structural variation and the mutational mechanisms underlying genomic disorders would be greatly improved by a genomewide map of hotspots of nonallelic homologous recombination (NAHR). Moreover, our understanding of sequence variation within the duplicated sequences that are substrates for NAHR lags far behind that of sequence variation within the single-copy portion of the genome. Perhaps the best-characterized NAHR hotspot lies within the 24-kb-long Charcot-Marie-Tooth disease type 1A (CMT1A)-repeats (REPs) that sponsor deletions and duplications that cause peripheral neuropathies. We investigated structural and sequence diversity within the CMT1A-REPs, both within and between species. We discovered a high frequency of retroelement insertions, accelerated sequence evolution after duplication, extensive paralogous gene conversion, and a greater than twofold enrichment of SNPs in humans relative to the genome average. We identified an allelic recombination hotspot underlying the known NAHR hotspot, which suggests that the two processes are intimately related. Finally, we used our data to develop a novel method for inferring the location of an NAHR hotspot from sequence variation within segmental duplications and applied it to identify a putative NAHR hotspot within the LCR22 repeats that sponsor velocardiofacial syndrome deletions. We propose that a large-scale project to map sequence variation within segmental duplications would reveal a wealth of novel chromosomal-rearrangement hotspots.