The phrase "small deletions" refers to the removal or elimination of a small part or piece from something. It means taking out a small portion or section of something, leaving the rest unchanged. Full definition
«I saw a relatively small deletion in the X chromosome, identified as Xp11.22; it had only a few genes in it. (sciencedaily.com)
When genetic messages get jumbled with small deletions like this, cells have machinery for recognizing the errors and ignoring their contents. (en.hdbuzz.net)
SV40 mutants with small deletions or base substitutions have been isolated by in vitro site - specific or random local mutagenesis of recombinant DNA followed by cloning in E. coli. (science.sciencemag.org)