HE mutant strain of the screw-worm fly (Cochliomyia hominivorax) known as Brc (black R-cell) was discovered in our laboratory almost two years ago, and has been maintained for over 20 generations. Earlier studies indicated that a dominant autosomal factor was involved. Appropriate tests indicated that penetrance of the mutation was excellent, but continued selection did not result in the establishment of a pure-breeding strain. Preliminary studies of the offspring from Brc x Brc indicated that the homozygous condition might render them viable but sterile. Further studies proved this hypothesis to be false and showed that the mutant phenotype was associated with a reciprocal translocation, that the homozygous condition was lethal, and that the aberrant segregation ratios were due to the occurrence of nonrandom segregation of the chromosomes at first meiotic metaphase in translocation heterozygotes. The genetic and cytological studies leading to these conclusions are herein presented. MATERIALS AND METHODSCochliomyia hominivorax (=Callitroga hominivorax) is an obligate parasite of warm-blooded animals. The biology and laboratory rearing procedures were discussed in several publications (MELVIN and BUSHLAND 1941; BUSHLAND 1960a, b). All flies used in these studies were reared on artificial media, allowed to pupate in sand or sawdust, and the adults were kept in wire mesh cages with honey and water as food. Colonies were maintained at 80°F. Other experimental procedures are described in connection with the tests in which they were employed.The term "Brc flies" denotes adults which have the mutant phenotype due to a dominant factor, but use of the term implies no distinction between heterozygotes and possible homozygotes. RESULTS Origin and phenotype of the Brc mutation:The mutation is characterized by having the entire R-cell in the wing completely blackened by dense pigmentation (Figure 1). The mutant flies have excellent vigor and appear normal in all other respects. The mutant strain was derived from a single male found among the progeny of irradiated flies. The mutant male was crossed to wild-type females
is generally recognized that certain types of chemicals cause biological effects I z o s e l y resembling those produced by radiation. Among these effects are the production of mutations, chromosome aberrations, and induction of sterility and cancer in animals. Our interest has been mainly to determine the effect of gamma radiation and alkylating agents upon growth and maturation of insect reproductive cells and the production of sterility by inducing dominant lethal mutations in these cells. In undertaking the studies reported herein we had several immediate objectives: ( 1 ) To determine dose-response curves for induction of dominant lethal mutations by either radiation or tretamine (2,4,6-tris (I-aziridinyl) -striazine) in meiotic oocytes and mature sperm for comparison of slopes, reaction kinetics and median lethal doses; (2) to compare response of different cell stages to either mutagen; and (3) to derive preliminary information from dose-response curves for later tests to determine potentiation of one agent by the other. No published study has come to our attention in which an inquiry was made into the combined action of a chemical mutagen and radiation in the induction of dominant lethal mutations. MATERIALS A N D METHODSAdult male and female screw-worm flies, Cochliomyia hominiuorax (Coquerel) (Diptera: Calliphoridae), were used in these experiments. The female reproductive system contains two ovaries, each consisting of 100 to 150 ovarioles in which egg development occurs synchronously. By treating one female, hundreds of oocytes, all in the same stage of development, are simultanzously exposed to the treatment. Gravid females deposit 200 to 250 eggs in a sagle mass.Three-day-old females reared at 80°F contain oocytes with the nucleus in early prophase of the first meiotic division, 4-day-old females contain almost fully mature eggs with the nucleus in metaphas2 I, and 5-day-old females contain a large number of fully mature eggs in which meiosis has progressed up to early anaphase I (LACHANCE and LEVERICH 1962). Further growth and changes in the egg and its nucleus are arrested in this stage until the egg is laid. Thus, the induction of dominant lethal mutations in meiotic oocytes can be detected by treating virgin females, mating them to untreated males, and scoring the hatchability of the eggs produced. Similarly, dominant lethal mutations in mature sperm are detected by treating 1-day-old males and allowing a single mating between treated males and normal females. Present address. Metabolism and Radiation Research Laboratory, State Cnirersity Station, Fargo, North Dakuta i8103.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.