Induction of Genetically Recombinant Chromosomes in the Absence of Induced Mutation

Abstract

GENETICALLY recombinant chromosomes can be induced (at a low frequency) in the Drosophila melanogaster male, although crossing-over does not usually occur in the male. The agents which have been shown to induce crossing-over are all mutagens (for example, formaldehyde^1–3, diethyl sulphate⁴, nitrogen mustard⁵, dihydroxydimethylperoxide⁶, X-rays⁷ and γ-rays⁸). It is therefore difficult in general to exclude the loss of a coupled genetic marker by mutation or by chromosomal deletion over one (or more) of the genetic markers. Usually, the latter event is operationally defined by lethality of the homozygote for the apparently recombinant chromosome, although the simultaneous presence of an independent recessive lethal mutation cannot necessarily be ruled out.