A frameshift mutation in which an A in the penultimate codon of ssep is substituted by an insertion of GT, resulting in a Y254V substitution and an addition of 21 amino acids to the carboxy terminus.
Homozygous males are fertile, but their progeny show paternal chromosome loss (loss rate of chromosome 4 is 10%). The timing of the chromosome loss has not been determined but there is no cytological evidence for chromosome loss during spermatogenesis.