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Exome sequencing has emerged as an economical way of focusing DNA sequencing efforts on the most functionally understood regions of the genome. Pre-capture pooling, where one bait library is used to pull down the exonic regions of several pooled samples simultaneously is a further financial improvement.
However, rare alleles in the pool might not be able to attract baits at the same rate as reference conform sequences can, and may hence be underrepresented. We investigated this potential issue by sequencing a hapmap family (4 individuals) using the pre-capture protocol from Illumina and Nimblegen. We did not observe clear evidence that heterozygote variants are missed but noted a trend for indels to be imbalanced.
Our findings do not provide clear evidence to rule out allelic imbalance or bias having an impact on research findings, this may be especially critical for low cellular cancer tissue where rare alleles are more ubiquitous.