Spectrum of visible mutations isolated out of wild populations of Drosophila melanogaster in 2000.

 

Weisman, N.Ya, I.D. Erokhina, and I.K. Zakharov.  Institute of Cytology and Genetics of Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090, Russia;  E-mail: weisman@bionet.nsc.ru

            One of the tasks of experimental genetics of populations is estimation of genetic diversity in natural populations.  Within the frames of continuing traditional studies on monitoring of wild populations (Golubovsky et al., 1974;  Weisman et al., 1995;  Weisman and Zakharov, 1997), the present work is devoted to analysis of representative samples of flies from geographically remote populations of Drosophila melanogaster, as well as to analysis and identification of visible mutations.

            Drosophila melanogaster from nature were collected in two regions of Russia: from Altai, populations Askat and Belokurikha; and from Republic of Udmurtia, populations Izhevsk, Karambai, and Pyuchas.  The samples consisted of 160-941 individuals.  For isolation of iso-female strains and their subsequent analysis of families, 50 fertilized in nature females were randomly selected.

            Mutations with similar phenotypes from a single population and from different populations were tested for allelism.  Linkage groups for each of the isolated mutations were determined by means of marked chromosomes 1, 2, and 3 laboratory strains, C(1)DX,ywf; B w^a/Y, and Cy/L;D/Sb, respectively.  Identification of mutations was performed by using the strains of Drosophila melanogaster with the known genotype from the foundation of Laboratory of Genetics of Populations of the Institute of Cytology and Genetics SB RAS.  Each of the isolated mutations is maintained in culture as a homozygous strain or as a strain with the balanced chromosome.

            Males and females of Drosophila melanogaster caught from nature were mostly of wild type phenotype.  However, in Izhevsk population, we have observed high concentration of flies with slight disruptions of abdomen segmentation (14% females, 2% males).  The females with the similar phenotype were found within the limits of 1% in two other populations from Republic of Udmurtia.  With the frequency of 1%, the males were found with brown eyes in populations from Askat and Karambai.

            In addition to aberrations found in flies that were caught directly from nature, by familial analysis of F₁ and F₂ in 5 populations, we have determined some other inherited modifications of a phenotype (see Table 1).  In all populations studied, the share of females, which offspring carry visible recessive mutations, is rather high, up to 20-40%.  Studying of the offspring of relatively small samples of flies enabled us to isolate from 6 to 10 different types of visible mutations, some of them multiply occurring in the population.  The great majority of isolated mutations were recessive, except the single dominant mutation, i.e., brown eyes from Karambai.  The population from Izhevsk is characterized not only by the highest concentration of visible mutations, but also by their most broad spectrum.

            Note that geographically remote populations, as a rule, possess by sets of mutations of different genes.  Only a single mutation of the chromosome 3, with eye color alteration (dark-red eyes), was found both in Izhevsk and Pyuchas.  Some aberrations were found with particularly high frequency, namely, disruption of abdomen segmentation in Askat and Karambai; as well as mutations of the chromosome 3, reduction of bristles and rough eyes in Izhevsk and mutation ebony in Belokurikha.

            In some families, several mutations were isolated.  For example, in the family А35 from Askat population, forked- and white-Х chromosomes were found simultaneously; whereas in Belokurikha - ebony and brown (family B7); and in Pyuchas population, mutation ‘bright eyes’ and ‘rudimental wings’ (family P24).  In the offspring of a single female from Karambai population (family К3), mutations of two genes that determine brown and red matted colour of eyes were found.  In the families from Izhevsk population, two or more inherited alterations were found simultaneously: stabbloid and detached (family I47); strow and ‘wing cuttings’ (family I50); ‘rough eyes’, ‘reduction of bristles’, and ‘wing cuttings’ (family I40).  Mutations ‘rough eyes’ and ‘reduction of bristles’ from Izhevsk population, in all 9 cases were found in the same chromosome 3.

            Note, in all five populations studied, the most frequently occurring mutations were those modifying the eye colour.  It is necessary to note distribution in all populations of inherited disruptions, with different extent of penetration, of abdomen segmentation.  However, genetic analysis of this aberration is not performed yet.  It could be supposed that relationship between our results and observations made by R.L. Berg, who has noticed since 1968 sharp increase in concentration of abnormalities similar to mutation abnormal abdomen (Berg, 1972a,b;  Golubovsky et al., 1974).

            Alleles of some known genes isolated from nature were shown to have some peculiarities of penetration.  For instance, the mutants ebony from Belokurikha and Askat have more dark colored body than that of flies of laboratory strain ebony.  In addition to this observation, in ebony homozygotes from Askat, the stigma in larvae were uncolored.  The mutants black from Karambai were also more light by color than that of “homonyms” from the strain maintained in fund collection.

            The novel recessive allele of the gene net (net-B27) from population Belokurikha has a homozygous penetration in a form of additional vein fragment at the 3rd dorsal wing compartment near by middle of the anal longitudinal vein.  This allele has incomplete penetration and varying expression.  In heterozygote with the standard net allele (Lindsley and Zimm, 1992), the allele net-27B is dominant.

            Acknowledgments:  The authors are grateful to Ivannikov A.V., Zakharenko L.P., and Gunbin K.V. for collections of flies from populations of Drosophila melanogaster from nature and to Orlova G.V. for translation of the article into English.  The study is supported by Russian Foundation of Basic Research (RFBR) No. 99-04-49743.

References:  Golubovsky, M.D., Yu.N. Ivanov, I.K. Zakharov, and R.L. Berg 1974, Genetika (Russ.), 10 (4): 72-83;  Weisman, N.Ya., D.E. Koryakov, and I.K. Zakharov 1995, Dros. Inf. Serv.  76: 103-106;  Weisman, N.Ya., and I.K. Zakharov 1997, Dros. Inf. Serv.  78: 19-21;  Berg, R.L., 1972a, Dros. Inf. Serv.  48: 67-69;  Berg, R.L., 1972b, 48: 67;  Lindsley, D.L., and G.G. Zimm 1992, The Genome of Drosophila melanogaster.  San Diego, CA, Academic Press, Inc.