Intron length variation of the Adh gene in Brachyscome (Asteraceae).

Eighteen polymerase chain reaction (PCR) products of the partial sequence of the Adh (alcohol dehydrogenase) gene from 10 Brachyscome species were sequenced and compared. These products contained the 5' three fourths of exon 4 and whole sequences of intron 3. They varied extensively in length due to the differences in length of intron 3. A total of 10 long insertions were flanked by direct repeats of 5 to 12 bp sequences, indicating inserted elements. These inserted elements were classified into the following five categories based on nucleotide sequence characteristics and length; (1) a region homologous to that of 5S RNA genes (5S DNA), (2) A-rich structure at the 3' end-like short interspersed elements (SINEs) in animals, (3) a sequence of 280 bp with no characteristic features, (4) a sequence of 125 bp with no characteristic features, (5) termini of 11 bp inverted repeats flanked by 5 bp sequence of direct repeats characteristics of a transposon.