A TECHNIQUE FOR THE ANALYSIS OF EPISTATIC GENE ACTION II. THE APPLICATION OF THE METHOD

With a method based on probability of phenotypic ratios being produced by crosses involving two pairs of interacting genes, data from genetic studies of Impatiens Sultana Hook. f. (Balsaminaceae) were analysed. Nine genes postulated to control floral color are: P, purple; I and W, white; R, red; O, orange; F, fuchsia; D, red; E, red; S, salmon. Epistatic action was evaluated, but progeny counts were too small for linkage to be determined.     

Fate of DNA encoding hygromycin resistance after meiosis in transformed strains of Gibberella fujikuroi (Fusarium moniliforme)

Stability of foreign DNA transformed into a novel host is an important parameter in decisions to permit the release of genetically engineered microorganisms into the environment. Meiotic instability of transformed DNA has been reported in fungi such as Ascobolus, Aspergillus, and Neurospora. We used strains of Gibberella fujikuroi (Fusarium moniliforme) transformed with the hygr gene from Escherichia coli to study meiotic stability of foreign DNA in this plant pathogenic fungus. Crosses with single-copy transformants segregated hygr:hygs in a 1:1 manner consistent with that expected for a Mendelian locus in a haploid organism. Multicopy transformants, however, segregated hygr:hygs in a 1:2 manner that was not consistent with Mendelian expectations for a chromosomal marker, even though two unrelated auxotrophic nuclear genes were segregating normally. Segregation ratios in crosses in which hygr was introduced via the male parent did not differ significantly from crosses in which the transformed strain served as the female parent. Some of the sensitive progeny from the crosses with the multicopy transformants carried hygr sequences. When these phenotypically sensitive progeny were crossed with a wild-type strain that carried no hygr sequences, some of the progeny were phenotypically hygr. Some progeny from some crosses were more resistant to hygromycin than were their sibs or the transformant strains that served as their parents. Transformants passaged through a maize plant only rarely segregated progeny with the high levels of resistance. The mechanism underlying these genetic instabilities is not clear but may involve unequal crossing over or methylation or both. Further work with cloned genes with homology to sequences already present in the Fusarium genome is warranted.     

Fate of DNA encoding hygromycin resistance after meiosis in transformed strains of Gibberella fujikuroi (Fusarium moniliforme).

Stability of foreign DNA transformed into a novel host is an important parameter in decisions to permit the release of genetically engineered microorganisms into the environment. Meiotic instability of transformed DNA has been reported in fungi such as Ascobolus, Aspergillus, and Neurospora. We used strains of Gibberella fujikuroi (Fusarium moniliforme) transformed with the hygr gene from Escherichia coli to study meiotic stability of foreign DNA in this plant pathogenic fungus. Crosses with single-copy transformants segregated hygr:hygs in a 1:1 manner consistent with that expected for a Mendelian locus in a haploid organism. Multicopy transformants, however, segregated hygr:hygs in a 1:2 manner that was not consistent with Mendelian expectations for a chromosomal marker, even though two unrelated auxotrophic nuclear genes were segregating normally. Segregation ratios in crosses in which hygr was introduced via the male parent did not differ significantly from crosses in which the transformed strain served as the female parent. Some of the sensitive progeny from the crosses with the multicopy transformants carried hygr sequences. When these phenotypically sensitive progeny were crossed with a wild-type strain that carried no hygr sequences, some of the progeny were phenotypically hygr. Some progeny from some crosses were more resistant to hygromycin than were their sibs or the transformant strains that served as their parents. Transformants passaged through a maize plant only rarely segregated progeny with the high levels of resistance. The mechanism underlying these genetic instabilities is not clear but may involve unequal crossing over or methylation or both. Further work with cloned genes with homology to sequences already present in the Fusarium genome is warranted.     

IS ORGANELLE DNA STRICTLY MATERNALLY INHERITED? POWER ANALYSIS OF A BINOMIAL DISTRIBUTION

Although numerous exceptions are well known, organelle DNA is often exclusively or predominantly maternally inherited. In such cases, maternal inheritance is often documented by the study of progeny derived from crosses between parents with distinguishable organelle genotypes. These studies generally detect a single type of progeny, those containing organelles derived from only one of the parents; no progeny containing organelles derived either from the opposite parent or from both parents are found. However, in most cases the number of progeny examined is quite small. I present a simple binomial model of organelle inheritance to determine the power of such experiments to distinguish between the hypothesis of strict maternal inheritance and a more complex hypothesis involving the presence of both organelle types within a progeny array. Extremely large sample sizes of progeny are required to distinguish these two hypotheses with reasonable confidence when organelle transmission is not strictly maternal. As a result, studies involving simple progeny testing may be misleading. Larger samples, more complex breeding designs, or more sensitive molecular methods are required to document adequately strict maternal inheritance of organelles.     

DISTANCE-DEPENDENT REGULATION OF STAMEN NUMBER IN CROSSES OF SCLERANTHUS ANNUUS (CARYOPHYLLACEAE) FROM A DISCONTINUOUS POPULATION

Scleranthus annuus is a highly inbreeding annual that has varying numbers of fertile stamens per flower. Two stamen-positions always have fully fertile stamens, whereas the other eight carry staminoids or stamens to varying degrees. I measured male expression in progeny produced by crossing individuals growing in a discontinuous population. Four types of progeny were analyzed: from self-pollinations, from cross-pollinations within a patch, from cross-pollinations between patches, and from cross-pollinations between populations. Selfed progeny showed the lowest total male fertility (25.8), followed by between-population crosses (26.7), between-patch crosses (27.4), and within-patch crosses (27.8). The effect of crossing, as measured by the relative increase in frequency of fully fertile stamens compared to selfed progeny, is highest for within-patch crosses and declines with increasing spatial separation between parents. The increase was strongest for one of the antipetalous stamen positions in progeny produced by between-patch crosses (490%). The response to crossing measured as an increase in stamen fertility was not the same for all ten stamen positions. A strong increase of fertile stamens is noted in all types of crossed progeny for the five stamen positions in the outer whorl (antipetalous stamens), positions that in selfed progeny carry staminoids. The three positions in the inner whorl that are not occupied by fully fertile stamens show varying responses to crossing.     

The effect of mating behaviour on progeny sex ratio of Mastrus ridens (Hymenoptera: Ichneumonidae), a biological control agent of codling moth

Mastrus ridens (Horstmann) (Hymenoptera: Ichneumonidae) was imported into quarantine as a potential biocontrol agent for codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae). Mating behaviour of the parasitoid and its effect on progeny sex ratio (as a proportion of males) were studied to help sustain the laboratory culture. Both females and males were reproductively active soon after emergence. Unmated females produced only male progeny, confirming males developed from unfertilized eggs. The proportion of males in a progeny was independent of the copulation period (24–40 s) of the parents. The progeny sex ratios from three parent ratios (f:m 2:1, 1:1 and 1:2) were not significantly different. Females effectively mated only once but males mated frequently in their lifetime. The progeny sex ratios from single females with a known single mating and possible multiple matings (through exposure to two males for 18 days) were not significantly different. However, when males copulated with five virgin females in sequence over a 2 h period, the fifth female produced more males than the preceding four, presumably due to sperm depletion. Results of this study provide data on progeny sex allocation of M. ridens that help to prevent the development of a male-biased sex ratio that could threaten the maintenance of the culture over time.     

Effects of parent age at mating on reproductive response of Glyptapanteles flavicoxis (Hymenoptera: Braconidae), a larval parasitoid of the gypsy moth (Lepidoptera: Lymantriidae)

Glyptapanteles flavicoxis (Marsh) (Hymenoptera: Braconidae) is a gregarious larval parasitoid of the Indian gypsy moth Lymantria obfuscata (Walker) (Lepidoptera: Lymantriidae), that is believed to have potential for inundative releases against gypsy moth populations, because it can be reared in large numbers with few hosts. Unfortunately, sex ratios in laboratory reared G. flavicoxis are usually male-biased, hindering efforts to mass release this species for biological control by making the production of females costly. Because parental age at time of mating is known to affect the sex ratio in some Braconidae, we crossed haploid males and virgin females at 0, 1, 4, 9, and 16 d old with at least 10 trials for each of the 25 combinations. Numbers and sex ratios of progeny produced by females each day were recorded. Both progeny and sex ratios (percentage of females) among progeny produced by ovipositing females of G. flavicoxis decreased markedly over time, so only the first days production need be used in mass rearing. The reduction in the proportion and numbers of females among progeny as females aged is consistent with sperm depletion. Approximately 30% of females in all age classes mated to newly emerged males (day 0) produced all male progeny, whereas only 10-15% of those mated to older males failed to produce any daughters. When crosses with only male progeny were excluded from the analysis, females mated to males 1 d old had higher sex ratios in progeny than those mated to males in other age classes. In addition, females mated the day that they emerged tended to have progeny with the highest sex ratios.     

谷蠹和米象对磷化氢抗性遗传的研究

本文就谷蠹Rhyzopertha dominica 和米象Sitophilus oryzae对磷化氢的抗性遗传进行了研究,分别对两个种的实验室敏感品系和粮仓现场采集的抗性品系作为亲本进行杂交。同时测定了各自的亲本及其F₁杂种、F₁对抗性亲本回交和F2混交后代的剂量-死亡率反应曲线,并对它们的结果进行了遗传分析。结果指出,谷蠹和米象的F₁杂种对磷化氢的抗性遗传都为不完全隐性,各自的显性度(D)分别是-0.768和-0.348。同时F₁,回交和F₂混交的观察值和计算值之间的X²分析也表明,抗性表现为一个以上的常染色体因子遗传,但是主要是受隐性因子所控制。     

GENETIC ANALYSIS OF DEVELOPMENTAL MECHANISMS IN HYDRA I. SEXUAL REPRODUCTION OF HYDRA MAGNIPAPILLATA AND ISOLATION OF MUTANTS

Hydra magnipapillata strains collected from various localities in Japan were induced to reproduce sexually.
From the survival data of the progeny, it was calculated that H. magnipapillata contained an average of between 3.5 and 4.0 lethal equivalent units of recessive deleterious genes per gamate (between 7.0 and 8.0 per animal).
Various types of developmental mutants were found among the offspring of crosses made between strains isolated from the same ponds. The mutant types isolated included mini strains, maxi strains, multi-headed strains, nematocyst-deficient strains, regeneration-deficient strains and male sterile strains. The characters of these strains were stably transmissible to the successive progeny produced by budding. These strains therefore were propagated by budding and maintained as clonal lines to be used later for developmental studies.     

Inheritance of microsatellite DNA in bisexual gynogenesis complex of Fangzheng silver crucian carp,Carassius auratus gibelio (Bloch)

Five gynogenetic progeny groups of silver crucian carp Carassius auratus gibelio were produced and sex ratios (males:total progeny) of each of the progeny groups were analysed. About 110 males and 366 females were genotyped at 15 microsatellite loci for comparison with their parents to (1) verify the gynogenesis status of Fangzheng C. auratus gibelio, (2) detect the incorporation of paternal genetic material into the offspring and (3) study the possible association of genetic exchange at microsatellite loci with the existence of sex. The sex ratios in progenies of five groups were highly variable, but all had significant female bias. The sex ratio ranged from 0 to 0·37. Significant differences in the sex ratio within and between groups were also found. Microsatellite genotyping at 15 loci showed that 100 and 97% of the progeny shared the same genotype with the mother in four groups and in one group, respectively, confirming that gynogenesis is the general mechanism of reproduction in C. auratus gibelio. However, 0·63% of all offspring did show incorporation of paternal genetic material. No single loci tested were associated with the occurrence of male progeny, indicating unknown genetic mechanisms for sex determination in C. auratus gibelio.     

ANALYSIS OF THE GEOTROPIC ORIENTATION OF YOUNG RATS. IX

Adult hybrid rats from the cross of races A x B show a total capacity to vary their geotropic performance which is identical with that of their B parents. The proportionate modifiable variability of geotropic orientation also agrees quantitatively with that for the B parents. These relationships are not disturbed by the action of adrenin, which leads to a distortion of the θ vs. α curve. Young rats of the F ₁ generation show a greater proportion of unmodifiable variation of geotropic orientation. It is pointed out that the present findings support the conclusion that the capacity of rats to exhibit variation of geotropic orientation is limited by their genetically determined composition and that the special condition in the young hybrids may be understood as due to a kind of temporary disharmony of developmental events.     

A transgenic, mesodermal specific, Dkk1 mouse model recapitulates a spectrum of human congenital limb reduction defects

Congenital limb reduction defects occurring in isolation of other developmental abnormalities continue to be an important medical problem in which little progress has been made. Herein we generated transgenic mice expressing Dkk1 in an appendicular mesodermal pattern. Prx1-Dkk1 mice recapitulate a full spectrum of human congenital limb reduction defects, without other developmental issues, and have normal life-spans. Importantly, a close examination of the inheritance pattern suggests that there is a significant degree of incomplete penetrance as progeny of phenotypically positive or phenotypically negative, but genotypically positive Prx1-Dkk1 mice, consistently give rise to both phenotypically positive mice and phenotypically normal-appearing mice. Thus, this heterogeneous phenotype is reproducible with each generation regardless of the phenotype of the parents. We further go on to identify that mesenchymal stem cells from Prx1-Dkk1 mice have limited proliferative ability, but normal differentiation potential, which may explain the mechanism for the limb reduction defects observed. We believe Prx1-Dkk1 mice may prove useful in the future to study the mechanisms underlying the development of congenital limb reduction defects.     

Studies of four thelytokous puerto rican isolates ofMuscidifurax uniraptor [Hymenoptera: Pteromalidae]

Field collections in Puerto Rico revealed 4 behaviorally distinct isolates ofMuscidifurax uniraptor Kogan & Legner that differed initially in diapause and nondiapause emergence, and the age when ♀ progeny were produced. Subsequent F₁ and F₂ progeny differed in sex ratio and total progeny production. Mating F₂ ♀ ♀ from nondiapause isolates to naturally emerging ♂ ♂ from thelytokous populations significantly reduced total progeny and the proportion of ♀ ♀ toca. 20 %. These mated ♀ ♀ at first resembled in behavior those which originated from diapausing parents. Random mating within all isolates beginning in the F₃, resulted in a general lower survival and progeny production but was accompanied by a rise in sex ratio toca. 50% ♀ ♀ by the F₆ generation. The interinvolvement of extranuclear and genic factors is considered.      

Investigation of the het genes that control heterokaryon incompatibility between members of heterokaryon-compatibility (h-c) groups A and G1 of Aspergillus nidulans

A chromosome assay method was used to determine the heterokaryon compatibility relationships between strains belonging to heterokaryon-compatibility (h-c) groups A and G1 of Aspergillus nidulans. A hybrid strain (RD15) was isolated following protoplast fusion of strains 65-5 (h-cA) and 7-141 (h-cG1). The morphology of RD15 was severely abnormal compared to diploid strains of A. nidulans produced from heterokaryon-compatible haploid parents. Inocula of RD15 were induced to haploidize on medium containing Benlate and a parasexual progeny sample of 291 haploid segregants was obtained. The progeny strains were genotyped for standard markers. Allelic ratios and pairwise marker segregations were determined. Pairs of progeny strains that carried different alleles for the standard markers on each linkage group in turn were tested for compatibility. Strain pairs that possessed different alleles for the markers on linkage groups II, III, V, VI and VII were incompatible indicating the presence of heterokaryon-incompatible (het) genes on these linkage groups. Backcrosses to an h-cGl strain showed that two het genes were located on linkage group III and confirmed a total of six het gene differences between the h-cA and h-cGl strains.     

Effect of gametic disequilibrium on means and on genetic variances of autotetraploid synthetic varieties

Summary The occurrence and effects of a gametic disequilibrium (DSE) in the first generation of a theoretical two-population synthetic variety were investigated. Theoretical development was limited to the genetics at a single locus with two alleles in an autotetraploid species with random chromosome inheritance. Algebraic expressions were developed for the differences between the mean genotypic values of the two-population synthetic variety at generation one and in random mating equilibrium (RME). For the situation where both parents of the synthetic were in RME, a numerical analysis was performed for all possible allele frequencies assuming the following types of genic action: monoplex dominance, partial monoplex dominance, duplex dominance, partial duplex dominance, and additive. The result indicated that with non-additive genic action the DSE could, in some cases, greatly depress or inflate the mean genotypic value of the first generation (Syn-1_(RME)). Thus, any change of means over advancing generations with loss of DSE could be positive or negative. When additive genic action was assumed, there was no effect associated with DSE and when both parents had the same allele frequencies there was no DSE. The DSE, with only a minor exception, decreased the genetic variance and in numerous cases forced it near zero. Expressions were developed for mean genotypic values of a first generation synthetic with DSE in one parent (Syn-1_(DSE/RME)) or both parents (Syn-1_(DSE)). The deviation of these means from those of Syn-1_(RME) was a function of digenic and quadragenic population effects. An inspection of the response equations for Syn-1_(RME) indicated that in a series of crosses with one common parent the rankings of first generation means would be the same as the ranking of populations at equilibrium though the individual means would be biased. More importantly with DSE of one or both parents there are situations when a ranking of first generation mean genotypic values would not reflect relative frequency of desirable alleles in the populations. These results indicate that statistical analyses and selections based on means of the Syn-1 generation can have an error which is not avoidable by improvement in precision of evaluation.Cooperative investigations of the Alfalfa Production Research Unit, United States Department of Agriculture, Agricultural Research Service, and the Nevada Agricultural Experiment Station, Reno, Nevada, USAPaper No. 590 Scientific Journal Series, Nevada Agricultural Experiment Station     

Host modification of chlamydiae: differential infectivity for cell monolayers of chlamydiae grown in eggs and monolayers.

Cell monolayer-grown chlamydiae (CGO) differed from egg-grown organisms (EGO) in their increased spontaneous infectivity relative to centrifuge-assisted infectivity for monolayers. For each population spontaneous: centrifuge-assisted infectivity ratios were constant over a wide dose range. Spontaneous infection increased linearly with time and could not be exhausted from either population by prolonged adsorption; there was no change in infectivity ratios in residual supernatants. Further, one passage of EGO through monolayers gave CGO with stable infectivity properties not increased by further cell passage yet reverting on a single passage in eggs. Spontaneous infection of monolayers with EGO gave progeny with the same infectivity ratios as monolayers infected with EGO by centrifugation. The change in properties following EGO infection of monolayers occurred prior to natural release from cells. We conclude that EGO and CGO are two phenotypically distinct, homogeneous populations. The two infection modes are not properties of subpopulations within EGO and CGO. The relationship of these observations on chlamydiae to other possible host-imposed phenomena is considered.     

Effects of synergists on toxicity of six insecticides in parasitoid Diaeretiella rapae (Hymenoptera: Aphidiidae)

The resistance to and the effects of synergists on the toxicity of six insecticides in Diaeretiella rapae (M'Intosh) (Hymenoptera: Aphidiidae), a parasitoid of vegetable aphid collected in Jianxin at Fuzhou-City, Fujian, China, were studied. In comparison with susceptible F21 progeny, the resistance ratios in resistant F0 parents were 27.6 for methamidophos, 20.8 for fipronil, 47.5 for avermectin, 3.3 for fenvalerate, 4.5 for cypermethrin, and 74.7 for imidacloprid. Piperonyl butoxide (PB), triphenyl phosphate (TPP), and diethyl maleate (DEM) were chosen to be applied in susceptible F21 progeny, as well as in resistant F11 progeny and F0 parents. Significant synergistic effects on the toxicity of the six insecticides were found by using PB, TPP, and DEM in F0 parents; on methamidophos, avermectin, and imidacloprid by PB, TPP, and DEM in F11 progeny; on fipronil by PB and DEM in F11 progeny; and on fenvalerate and cypermethrin by PB in F11 progeny. PB also showed significant synergism on the six insecticides in susceptible F21 progeny, although the synergism was far less in F21 progeny than those in resistant F0 parents. TPP and DEM showed little or no synergistic effects on the toxicity of the six insecticides in F21 progeny. Compared with TPP and DEM, the highest synergistic ratios of PB for methamidophos, fipronil, avermectin, fenvalerate, cypermethrin, and imidacloprid were observed in F0 parents, and F11 and F21 progeny. The resistance levels to methamidophos, fipronil, avermectin, fenvalerate, and cypermethrin could be inhibited strongly by applying PB in F0 parents. From the results, oxidative degradation is believed to play a critical role in resistance to methamidophos, fipronil, avermectin, fenvalerate, and cypermethrin in D. rapae. To a lesser extent, hydrolytic reactions also were partially involved in the resistance to these five insecticides by using the synergists PB, TPP, and DEM. However, although high synergism of PB, TPP, and DEM on imidacloprid was found, the resistance levels to imidacloprid remained high in the presence of PB, TPP, and DEM. The mediated detoxification of oxidative degradation and hydrolytic reactions was thought to be involved in the resistance to imidacloprid in F0 parents.     

THE GENETIC CONTROL OF PATHOGENICITY,SEROTYPES AND VARIABILITY IN PUCCINIA SORGHI

Flangas , A. L., and J. G. Dickson . (U. Wisconsin, Madison.) The genetic control of pathogenicity, serotypes and variability in Puccinia sorghi. Amer. Jour. Bot. 48(4): 275–285. Illus. 1961.—Four urediospore clones of P. sorghi were inbred through the alternate host, Oxalis, and the recombinant lines were compared with the mother clones for changes in pathogenicity and serological reaction. The aecial, inbred recombinant lines were scored for pathogenicity on 6 inbred lines of maize, 4 of which contained single, dominant alleles isolated from a single gene locus each conditioning differential rust reaction and Pop 35 and Pop 36, each with 2 recessive genes. The inbred, recombinant lines from each of the 4 mother clones reflected similar dimensional changes from original pathogenicity, that is, an ultimate gain or loss in host range or specificity. Based on reaction type incited on the 4 allelic differential hosts, continued inbreeding through 3 generations did not segregate homozygous pathogenic complements into distinct pathogenic biotypes. A similar array of pathogenic types was produced after each generation of inbreeding. The suppressed pathogenicity types in the dicaryotic line were revealed only through recombination. Hybridization between dicaryotic lines of selected pathogenic types of sibling and nonsibling pedigree confirmed the indeterminate nature of the pathogenic locus. The genetic basis of the commonly occurring mesothetic-X reaction (necrotic flecks and uredia of varying size surrounded by chlorotic and necrotic areas) is explained by the heterologous complementarity of fit of the interacting genic systems (genetic units). The heterologous mesothetic-X reactions offer ambiguous definition to the specificity state of the interaction and cannot be explained on the discrete gene-for-gene basis of rust reaction. Antisera produced from the pathogenic types differentiated the homologous from the heterologous combinations and revealed cross-reactions with P. graminis avenae. The comparative antigen constitution of the urediospore clones and the sibling recombinants thus far reveal a possible parallel existing between the modes of inheritance of pathogenic specificity and antigenic specificity.     

ANALYSIS OF THE GEOTROPIC ORIENTATION OF YOUNG RATS. II

1. Equations describing the geotropic orientation of young rats as a function of the inclination of the surface on which creeping take place, under standardized conditions, are found to be of similar form but with different values of the contained constants, when several different, genetically stabilized lines or races are compared. The values of these constants are characteristic for the several races. 2. The biological "reality" of the differences between young rats of two races, as given mathematical form in terms of these parameters and coefficients, can be submitted to radical test by investigating their behavior in inheritance. A simple result favorable to the inquiry would be decisive; a complex, non-clear result would not however be definitely unfavorable to the view that "real" differences in behavior are in question. The actual result is of a kind demonstrating (a) the efficiency of the original formulations, and (b), at the same time, the definite inheritance of certain quantitative aspects of geotropic behavior. 3. On the assumption that orientation on a sloping surface is achieved when, within a threshold difference, the tension-excitations on the two sides of the body (legs) are the same, the angle of oriented progression (θ) can be taken as a direct measure of the total excitation. This is consistent with the equation, accurately obeyed by our initial races, Δ cos θ/Δ sin α = - const., where α is the slope of the surface. 4. The total excitation of tension-receptors must be regarded as involving, over a gross interval of time, (1) the total array of receptors with thresholds below a certain value, a function of the stretching force, and (2) the frequency of change of tension. The latter, largely determined (it is assumed) by the frequency of stepping, should be proportional to the speed of progression. This speed is directly proportional to log sin α. Hence Δθ/Δ log sin α. plotted against sin α, should give a picture of the distribution of effective thresholds among the available tension-receptors in terms of the exciting component of gravity. For the races investigated this distribution can be resolved in each case into three groups. 5. A "variability number" is employed which permits the demonstration that the variability of θ as measured is (1) definitely controlled by α, and is (2) a characteristic number for each of the pure races used. 6. By attaching a weight to rats of one race it is found that Δθ/Δα is modified in a manner concordant with the assumption that the three "groups of sense organs" are in fact discrete. 7. In race K these three groups (I, II, III) are large, in race A, small (i, ii, iii). F₁ rats of the cross between these two races show i, ii, III. 8. F₁ individuals back-crossed to A give in the progeny two sorts of individuals, in equal numbers: i, ii, III and i, ii, iii. 9. F₁ individuals back-crossed to K are expected to give in the progeny four types of individuals, I, II; i, II; I, ii; i, ii. In the numbers available these classes are reasonably clear, and occur with equal frequency. 10. It is pointed out that these considerations imply a mode of definition of a gene somewhat different from that commonly employed by tacit assumption; namely, a definition of the effect in inheritance as a function of some controlling, independent variable.     

对氨基苯甲酸对牙龄卟啉单胞菌胰酶样蛋白酶活性的影响

目的：测定不同浓度PABA对牙龄卟啉单胞菌胰酶样蛋白酶（TLP）活性的影响,以探讨血链球菌在龈下菌微生态平衡中的作用。方法：在1/2浓度的BH培养基中加入不同浓度的PABA和一定浊度的P.gingivalis,行常规培养。测定培养物上清液和菌细胞中TLP活性及蛋白质含量,计算TLP的比活。结果：PABA对P.gingivalis TLP的比活产生促进作用。结论：PABA影响P.gingivalis TLP的活性提示血链球菌可能对龈下菌斑的微生态平衡具调节作用。