What is micro-allele or STR micro-variant?

Micro-allele is an STR with a fractional value, such as 14.2, rather than a whole integer. Micro-alleles are sometimes also referred to as microvariants, fractional markers or partial repeats. Fractional values frequently arise from a deletion, the mutational loss of one or more nucleotides. For example, if the segment being repeated is AGG, one of the triplets can mutate to AG, thus becoming a fractional repeat. Fractional values can also arise from insertions. The duplicated Y-STR markers DYS385 and DYS464 are particularly prone to partial repeats. If you look at the marker details for DYS385 and DYS464 on the Sorenson Molecular Genealogy Foundation website you will see that there are quite a few results that end in a .1, .2, or a .3. Many STRs have a repeating base pair sequence that is somewhere between 3 to 6 base pairs in length. If the allele value ends in .1 this means that an extra base has been added somewhere in the repeated sequence, possibly at the beginning or at the end of the sequence. If the allele value ends in .2 this means that two extra bases have been added somewhere in the repeated sequence. If the allele value ends in .3 this means that three extra bases have been added somewhere in the repeated sequence. #genetics #YSTR #microvariants #DNA #CODIS