Genetic Analysis of Rough Sheath1 Developmental Mutants of Maize

Maize Rough sheath1 (Rs1) mutants are dominant and cause a proliferation of sheath-like tissue at the base of the blade and throughout the ligular region. They also cause ligule displacement, a chaotic pattern of vasculature and abnormal cellular structure of vascular bundles. The affected region of Rs1-O leaves displays genetic and morphological attributes of both sheath and auricle, suggesting an overlap of these genetic programs. The rs1 locus maps approximately 26 map units distal to opaque2 (o2) on chromosome 7S, defining a new distal-most locus on the genetic map. Three mutant alleles, Rs1-O, Rs1-1025 and Rs1-Z, all display similar phenotypes. The mutations are completely dominant and the Rs1-O phenotype is not affected by dosage of the chromosome arm carrying the rs1(+) allele, indicating that these alleles are neomorphic. Analysis of genetic mosaics showed that the Rs1-O phenotype is non-cell-autonomous, suggesting that intercellular signals convey the phenotype. Rs1 mutant phenotypes are affected by modifiers present in particular genetic backgrounds. An enhancer of Rs1-O was identified; segregation data imply a single recessive gene, ers1. Rs1 mutants were also found to enhance the expression of unlinked rs2 and Rs4 mutants, suggesting that these mutations affect similar developmental processes. We discuss the phenotypic and genetic similarities between Rs1 and Knotted1 (Kn1) mutants that led to the identification of rs1 as a kn1-like homeobox gene (unpublished data).     

Genetic Analysis of Olfactory Behavior in Drosophila: A New Screen Yields the Ota Mutants

A simple means of measuring Drosophila olfactory response is described, and the behavior which it measures is characterized. The assay was used to screen for X-linked mutants defective in olfactory function. Six ota mutants were isolated and characterized (ota = olfactory trap abnormal). Four of the mutants were found to be abnormal in another chemosensory behavior as well. Two of the mutant phenotypes extend to include another sensory system: they are defective in visual system physiology. All were normal, however, in a test of giant fiber system physiology. Two of the mutations are dominant, and the recessive mutations define two complementation groups. Mutations representing each complementation group, as well as one of the dominant mutations, were mapped. For the mutants with defective visual system physiology, the visual defects were shown to cosegregate with olfactory phenotypes.     

Genetic Analysis of Flagellar Mutants in Escherichia coli

Flagellar mutants in Escherichia coli were obtained by selection for resistance to the flagellotropic phage chi. F elements covering various regions of the E. coli genome were then constructed, and, on the basis of the ability of these elements to restore flagellar function, the mutations were assigned to three regions of the E. coli chromosome. Region I is between trp and gal; region II is between uvrC and aroD; and region III is between his and uvrC. F elements carrying flagellar mutations were constructed. Stable merodiploid strains with a flagellar defect on the exogenote and another on the endogenote were then prepared. These merodiploids yielded information on the complementation behavior of mutations in a given region. Region III was shown to include at least six cistrons, A, B, C, D, E, and F. Region II was shown to include at least four cistrons, G, H, I, and J. Examination of the phenotypes of the mutants revealed that those with lesions in cistron E of region III produce "polyhooks" and lesions in cistron F of region III result in loss of ability to produce flagellin. Mutants with lesions in cistron J of region II were entirely paralyzed (mot) mutants. Genetic analysis of flagellar mutations in region III suggested that the mutations located in cistrons A, B, C, and E are closely linked and mutations in cistrons D and F are closely linked.     

Genetic Analysis of Dictyostelium Slug Phototaxis Mutants

Mapping and complementation analysis with 17 phototaxis mutations has established 11 complementation groups phoA-phoK distributed over six linkage groups. Statistical calculations from the complementation data yielded 17 as the maximum likelihood estimate of the number of pho genes assuming all loci are equally mutable. Most of the phototaxis mutants were found to exhibit bimodal phototaxis and all were found to be impaired in positive thermotaxis supporting convergence of the photosensory and thermosensory pathways. The thermotaxis mutant HPF228 was unaltered in phototaxis suggesting that the mutation in this strain affects a gene product whose site of action is before the convergence of the two pathways. Other phenotypes such as multiple tip formation by aggregates, stumpy fruiting bodies with short or absent stalks and short migration were associated with some pho alleles suggesting multiple biological roles for some gene products important in phototransduction.     

Origin of Chinese Goldfish and Sequential Loss of Genetic Diversity Accompanies New Breeds

Background

Goldfish, Carassius auratus, have experienced strong anthropogenic selection during their evolutionary history, generating a tremendous extent of morphological variation relative to that in native Carassius. To locate the geographic origin of goldfish, we analyzed nucleotide sequences from part of the control region (CR) and the entire cytochrome b (Cytb) mitochondrial DNA genes for 234 goldfish and a large series of native specimens. Four important morphological characteristics used in goldfish taxonomy–body shape, dorsal fin, eye shape, and tailfin–were selected for hypothesis-testing to identify those that better correspond to evolutionary history.

Principal Finding

Haplotypes of goldfish rooted in two sublineages (C5 and C6), which contained the haplotypes of native C. a. auratus from southern China. Values of F _ST and N_m revealed a close relationship between goldfish and native C. a. auratus from the lower Yangtze River. An extraordinary, stepwise loss of genetic diversity was detected from native fish to goldfish and from Grass-goldfish relative to other breeds. Significantly negative results for the tests of Tajima’s D and Fu and Li’s D* and F* were identified in goldfish, including the Grass breed. The results identified eye-shape as being the least informative character for grouping goldfish with respect to their evolutionary history. Fisher’s exact test identified matrilineal constraints on domestication.

Conclusions

Chinese goldfish have a matrilineal origin from native southern Chinese C. a. auratus, especially the lineages from the lower Yangtze River. Anthropogenic selection of the native Carassius eliminated aesthetically unappealing goldfish and this action appeared to be responsible for the stepwise decrease in genetic diversity of domesticated goldfish, a process similar to that reported for the domestication of pigs, rice, and maize. The three-breed taxonomy–Grass-goldfish, Egg-goldfish, and Wen-goldfish–better reflected the history of domestication.     

Genetic Analysis of Phenylalanine-Responding Mutants of Pseudomonas aeruginosa

A transduction analysis of phenylalanine-responding mutants of Pseudomonas aeruginosa revealed the existence of six unlinked genes. Enzyme assays showed that one gene was involved in the terminal production of phenylalanine (chorismate mutase), and the remaining five genes were involved in the common pathway of aromatic amino acid biosynthesis.     

Genetic Analysis of Long-Flagella Mutants of Chlamydomonas Reinhardtii

The length of the flagella of Chlamydomonas reinhardtii cells is tightly regulated; both short-flagella and long-flagella mutants have been described. This report characterizes ten long-flagella mutants, including five newly isolated mutants, to determine the number of different loci conferring this phenotype, and to study interactions of mutants at different loci. The mutants, each of which was recessive in heterozygous diploids with wild type, fall into three unlinked complementation groups. One of these defines a new gene, lf3, which maps near the centromere of linkage group I. The flagellar length distributions in populations of each mutant were broad, with the longest flagella measuring four times the length of the longest flagella seen on wild-type cells. Each of the ten mutants had defective flagellar regrowth after amputation. Some of the mutants showed no regrowth within the time required for wild-type cells to regenerate flagella completely. Other mutants had subpopulations with rapid regeneration kinetics, and subpopulations with no observable regeneration. The mutants were each crossed to wild type to form temporary quadriflagellate, dikaryon cells; in each case the long flagella were rapidly shortened in the presence of the wild-type cytoplasm, demonstrating that the mutants were recessive, and that length control could be exerted on already assembled flagella.     

Isolation and Genetic Analysis of Amber uvrA and uvrB Mutants

Genetic properties of amber uvrA and uvrB mutants of Escherichia coli K-12 are described. The isolation of three amber uvrA and two amber uvrB mutants indicates that the products of these genes are proteins.     

Genetic Analysis of Sex Chromosomal Meiotic Mutants in DROSOPHILA MELANOGASTER

A total of 209 ethyl methanesulfonate-treated X chromosomes were screened for meiotic mutants that either (1) increased sex or fourth chromosome nondisjunction at either meiotic division in males; (2) allowed recombination in such males; (3) increased nondisjunction of the X chromosome at either meiotic division in females; or (4) caused such females, when mated to males heterozygous for Segregation-Distorter (SD) and a sensitive homolog to alter the strength of meiotic drive in males.-Twenty male-specific meiotic mutants were found. Though the rates of nondisjunction differed, all twenty mutants were qualitatively similar in that (1) they alter the disjunction of the X chromosome from the Y chromosome; (2) among the recovered sex-chromosome exceptional progeny, there is a large excess of those derived from nullo-XY as compared to XY gametes; (3) there is a negative correlation between the frequency of sex-chromosome exceptional progeny and the frequency of males among the regular progeny. In their effects on meiosis these mutants are similar to In(1)sc(4L)sc(8R), which is deleted for the basal heterochromatin. These mutants, however, have normal phenotypes and viabilities when examined as X/0 males, and furthermore, a mapping of two of the mutants places them in the euchromatin of the X chromosome. It is suggested that these mutants are in genes whose products are involved in insuring the proper functioning of the basal pairing sites which are deleted in In(1)sc(4L)sc(8R), and in addition that there is a close connection, perhaps causal, between the disruption of normal X-Y pairing (and, therefore, disjunction) and the occurrence of meiotic drive in the male.-Eleven mutants were found which increased nondisjunction in females. These mutants were characterized as to (1) the division at which they acted; (2) their effect on recombination; (3) their dominance; (4) their effects on disjunction of all four chromosome pairs. Five female mutants caused a nonuniform decrease in recombination, being most pronounced in distal regions, and an increase in first division nondisjunction of all chromosome pairs. Their behavior is consistent with the hypothesis that these mutants are defective in a process which is a precondition for exchange. Two female mutants were allelic and caused a uniform reduction in recombination for all intervals (though to different extents for the two alleles) and an increase in first-division nondisjunction of all chromosomes. Limited recombination data suggest that these mutants do not alter coincidence, and thus, following the arguments of Sandler et al. (1968), are defective in exchange rather than a precondiiton for exchange. A single female mutant behaves in a manner that is consistent with it being a defect in a gene whose functioning is essential for distributive pairing. Three of the female meiotic mutants cause abnormal chromosome behavior at a number of times in meiosis. Thus, nondisjunction at both meiotic divisions is increased, recombinant chromosomes nondisjoin, and there is a polarized alteration in recombination.-The striking differences between the types of control of meiosis in the two sexes is discussed and attention is drawn to the possible similarities between (1) the disjunction functions of exchange and the process specified by the chromosome-specific male mutants; and (2) the prevention of functional aneuploid gamete formation by distributive disjunction and meiotic drive.     

Genetic and Developmental Analysis of the Locus vnd in DROSOPHILA MELANOGASTER

Genetic and developmental analysis of an X-linked vital locus vnd was undertaken. Embryos hemizygous for the original allele vnd did not hatch and exhibited a disorganized ventral nervous system (VNS). The mutation maps in the region 1B6-7 to 1B9-10, a subregion of an area previously shown to be essential to normal neural development. In this paper, we report isolation of five new alleles at the locus vnd. Genetic complementation analysis of all mutations at the vnd locus, with lethal alleles at adjacent loci, indicates that all lesions at the locus vnd affect only one vital gene function in the region. Four of the five alleles are embryonic lethal; one allele is subvital and behaves like an hypomorphic mutation. Hemizygous embryos for three of the four embryonic lethal alleles were inspected in histological sections; all exhibited disorganized VNS similar to the original allele. The developmental analysis in gynandromorphic genetic mosaics shows that (1) vnd+ gene function is not essential in most imaginal-disc cell derivatives, (2) only about 30% of the mosaic zygotes survive as adults, (3) mosaic zygotes with mutant tissue close to the head cuticle are least likely to survive, and (4) mutant tissue in the thoracic ganglion in the adult is not necessarily lethal. The mosaic data are consistent with the vnd+ gene function being necessary in neural cells derived from the anterioventral region of the blastoderm.     

拟南芥耐低钾突变体的筛选及遗传分析

利用乙酰甲基磺酸（ＥＭＳ）诱变方法,以幼苗根在重力作用下的弯曲生长为指标、筛选得到了拟南芥（Ａrabidopsis thaliana)耐低钾突变体。经过对突变体杂交后代的遗传分析证明,其中两株突变体的耐低钾性状为隐性单基因突变所致。鉴定、分离与植物耐低钾性状连锁的基因将有可能与对培育钾高效作物品种有重要意义。     

Comparative Analysis of Melanins and Melanosomes Produced by Various Coat Color Mutants

Pigmentation in the skin, hair, and eyes of animals is influenced by a number of genes that modulate the activity of melanocytes, the intervention of enzymatic controls at different stages of the melanogenic process, and the physico-chemical properties of the final pigment. The results of combined phenotypic, ultrastructural, biochemical, and chemical analyses of hairs of a variety of defined genotypes on a common genetic background performed in this study are consistent with the view that pigmentation of dark to black hairs results from the incorporation of eumelanin pigments whereas that of yellow hairs results from the incorporation of eu- and pheomelanins. It is also clear that relatively minor differences in melanin content can have dramatic effects on visible hair color. A good correlation was found for expression of (and enzyme activities associated with) TRP1 and TRP2 with eumelanin synthesis and eumelanosome production.     

Genetic Analysis of Temperature-Sensitive Lethal Mutants of Salmonella Typhimurium

We have isolated 440 mutants of Salmonella typhimurium that show temperature-sensitive growth on complex medium at 44 degrees. Approximately 16% of the mutations in these strains have been mapped to 17 chromosomal locations; two of these chromosomal locations seem to include several essential genes. Genetic analysis of the mutations suggests that the collection saturates the genes readily mutable to a ts lethal phenotype in S. typhimurium. Physiological characteristics of the ts lethal mutants were tested: 6% of the mutants can grow at high temperature under anaerobic conditions, 17% can grow when the medium includes 0.5 M KCl, and 9% of the mutants die after a 2-hr incubation at the nonpermissive temperature. Most ts lethal mutations in this collection probably affect genes required for growth at all temperatures (not merely during high temperature growth) since Tn10 insertions that cause a temperature-sensitive lethal phenotype are rare.