Two mutant strains of Drosophila melanogaster, pero1 (arrhythmic) and pers (short period), were mapped to determine the location and nature of these mutations. The authors isolated and digested the mutated DNA fragments from pero1 and pers flies via restriction mapping and vector cloning. Mutant or wildtype vectors were then transduced into pero1 flies to assess changes in circadian behaviour.
Cloning of different sized fragments of per DNA mapped both mutations to a 1.7kb region of the per gene. Sequencing of these fragments revealed the pero1 mutation site as a single nucleotide C-to-T substitution, resulting in a stop codon in exon 4 and a truncated protein. The pers mutation was identified as a G-to-A substitution, resulting in a single amino acid missense mutation.