We speculate that, since this is a weaker allele, the MB06458 insertion may affect Alk expression in a subtle or more restricted, tissue-specific manner. Flies transheterozygous for f01491and MB06458 were small and sickly and could therefore not be tested behaviorally; these data show, however, that the two P element insertions are allelic. We also crossed heterozygous flies carrying the Alk1 allele [27], which expresses a truncated protein and is an ALK functional null, with heterozygous f01491 mutant flies. We were unable to recover any transheterozygous Alk1/f01491 mutants, indicating a failure of these mutations to complement.
