§ 798.5275 Sex-linked recessive lethal test in drosophila melanogaster.
(a) Purpose. The sex-linked recessive lethal (SLRL) test using Drosophila melanogaster detects the occurrence of mutations, both point mutations and small deletions, in the germ line of the insect. This test is a forward mutation assay capable of screening for mutations at about 800 loci on the X-chromosome. This represents about 80 percent of all X-chromosome loci. The X-chromosome represents approximately one-fifth of the entire haploid genome.
(b) Definitions. (1) Lethal mutation is a change in the genome which, when expressed, causes death to the carrier.
(2) Recessive mutation is a change in the genome which is expressed in the homozygous or hemizygous condition.
(3) Sex-Linked genes are present on the sex (X or Y) chromosomes. Sex-linked genes in the context of this guideline refer only to those located on the X-chromosome.
(c) Reference substances. These may include, but need not be limited to, ethyl methanesulfonate or N-nitroso-dimethylamine.
(d) Test method—(1) Principle. Mutations in the X-chromosome of D. melanogaster are phenotypically expressed in males carrying the mutant gene. When the mutation is lethal in the hemizygous condition, its presence is inferred from the absence of one class of male offspring out of the two that are normally produced by a heterozygous female. The SLRL test takes advantage of these facts by means of specially marked and arranged chromosomes.
(2) Description. Wild-type males are treated and mated to appropriate females. Female offspring are mated individually to their brothers, and in the next generation the progeny from each separate dose are scored for phenotypically wild-type males. Absence of these males indicates that a sex-linked recessive lethal mutation has occurred in a germ cell of the P1 male.