DNA nullomers as a statistical phenomenon

Abstract

Nullomers are sequences absent from a certain genome. Due to their unexpected occurrence in short sequences, a hypothesis is that they are avoided for evolutionary reasons or because they might have lethal consequences on organisms. However, we present evidence that the occurrence and frequency of nullomers in genomes is expected as a stochastic consequence of uneven base pair combination distributions in the genetic code. This is done by artificially constructing whole genomes from statistics with a Markov chain model. The number of nullomers in these artificial genomes is in good agreement with the nullomer counts in reference genomes. Additionally, we investigated the nullomers of over 200 human genomes and found large deviations in the nullomers between individuals, further supporting the hypothesis that a vast majority of nullomers is very unlikely to have lethal effects.