genotyping error

[mel]

I m working with microsatellite markers and I know that genotyping errors like allelic dropouts are often accpected. However, I know how the loss of longer alleles occure, but wich reasons are thinkable if the shorter alleles are not detected?

[Niqqie]

There could be a mutation (in that individual) at the site the primer is supposed to bind, this way one allele might not amplify.