Oxidative phosphorylation was studied in mitochondria isolated from whole 72-hour larvae heterozygous for nine different Minute mutants with loci on the second and third chromosomes, i.e: M(2)12, M(2)1, M(2)173, M(2)z, M(3)w, M(3)124, M(3)B2, M(3)y and M ( 3 ) l .In all Minutes, oxidative phosphorylation was found to be abnormal in that phosphorylation was uncoupled from oxygen uptake to a greater extent as compared to controls. Differences with respect to respiration and/or phosphorylation were also evident between the Minutes themselves. The results strengthen the hypothesis that lesions in oxidative phosphorylation are associated with the Minute phenotype and demonstrate genetic control over this basic cellular process. In addition, if it is assumed that the Minutes are heterochromatic, as believed by many investigators, then the present study indicates a physiological function for heterochromatin.

inutes of Drosophila melanogaster include a large group of factors which THE are dominant over wild type when heterozygous, and lethal when homozygous.All heterozygous Minutes are characterized by the presence of short, slender bristles in the adult and by a retardation in development in larval life. Although the Minutes mimic one another in expression, they have been found to occupy a variety of loci in all four chromosomes and are considered by most authors to be chromosomal deficiencies (BRIDGES and BREHME 1944). The behavior of these factors when combined with modifiers or with other Minutes has indicated that many are qualitatively different (SCHULTZ 1929).The purpose of the present study is to determine whether or not different Minutes, so similar in heterozygous phenotype, also resemble one another with respect to homozygous phenotype. This investigation is concerned with an analysis of the factors responsible for the death of individuals homozygous for seven different Minutes, one of which, M ( l ) o , is located on the X chromosome; two, M(Z)l and M(Z)P, are overlapping deficiencies of the second chromosome; while the other four, M(3)w, M(3)124, M ( 3 ) B and M(3)B2, comprise an allelic series of the third chromosome. Some information concerning these different Minutes is available in the literature and will be reviewed briefly in the following section.Minute (1)o resembles other members of the Minute series in that heterozygous females possess smaller bristles and a longer larval developmental period than the wild type. This mutant is lethal in males. Salivary chromosome studies have shown Supported by a grant-in-aid from the American Cancer Society-on recommendation of the Committee on Growth of the National Research Council.