Chromosome Interactions in DROSOPHILA MELANOGASTER. II. Total Fitness

In a large experiment, using nearly 200 population cages, we have measured the fitness of Drosophila melanogaster homozygous (1) for the second chromosome, (2) for the third chromosome, and (3) for both chromosomes. Twentyfour second chromosomes and 24 third chromosomes sampled from a natural population were tested. The mean fitness of the homozygous flies is 0.081 ± 0.014 for the second chromosome, 0.080 ± 0.017 for the third chromosome, and 0.079 ± 0.024 for both chromosomes simultaneously. Assuming that fitnesses are multiplicative (the additive fitness model makes no sense in the present case because of the large selection coefficients involved), the expected mean fitness of the homozygotes for both chromosomes is 0.0066; their observed fitness is more than ten times greater. Thus, it appears that synergistic interactions between loci are considerable; and that, consequently, the fitness function substantially departs from linearity. Two models are tentatively suggested for the fitness function: a "threshold" model and a "synergistic" model.—The experiments reported here confirm previous results showing that the concealed genetic load present in natural populations of Drosophila is sufficient to account for the selective maintenance of numerous polymorphisms (of the order of 1000).     

Genotype-Temperature Interaction in DROSOPHILA MELANOGASTER. II. Body Weight

The effect of genotype-temperature interactions on body weight has been studied in a natural population of Drosophila melanogaster using four isogenic strains derived from it, and their hybrid F(1) and F(2) progenies. Measurements were made at four constant temperatures-25 degrees , 21 degrees , 17 degrees and 13 degrees C-and at a temperature oscillating between 17 degrees and 25 degrees C.-Low, though significant, genotype-temperature interaction exists among the isogenic strains, but not among the F(1) nor F(2) hybrid progenies. These low interaction values may be due to the fact that all isogenic strains have a common origin and therefore presumably little genic divergence exists among them. F(1) and F(2) hybrid progenies generally exhibit higher homeostasis than the isogenic strains, although one isogenic line has better homeostasis than the majority of the hybrids.-There is no evidence of heterosis and some evidence of dominance. These results are consistent with the hypothesis that body weight is regulated mainly by additive genetic factors and is subject to stabilizing selection.     

Meiosis in Male DROSOPHILA MELANOGASTER. II. Nonrandom Segregation of Compound-Second Chromosomes

The segregation of compound-second chromosomes in males from two different stocks has been examined. Segregation is random in males from the C(2L)RM4, dp; C(2R)RM4, px stock. Gametes containing only one of the two compound chromosomes comprise 50% of the gametes, and gametes containing either both elements or neither element make up the other 50% of the gametes.——In males from the C(2L)RM, b; C(2R)RM, cn stock, gametes containing either C(2L)RM, b or C(2R)RM, cn make up the majority of the gametes. Gametes containing both chromosomes or neither chromosome account for only 2-3% of the gametes. The nonrandom segregation is due to the C(2R)RM, cn chromosome.——Viability is reduced in flies carrying the C(2R)RM, cn chromosome. This includes larval lethality, delayed development and premature adult lethality. Cytologically, this chromosome contains a large duplication of 2L material, which includes material proximal to region 38 or 39. It is suggested that the viability and segregational properties associated with this chromosome are due to the duplicated 2L material.     

Genetic Change of Recombination Value in DROSOPHILA MELANOGASTER. II. Simulated Natural Selection

Selection of Gl-Sb coupling heterozygotes was carried out for more than one hundred generations commencing with six independent lines drawn from a common base population. Population sizes were eight, sixteen and forty-eight parents per generation. The effect of natural selection on recombination value was measured by sampling and testing females at varying intervals of time. There was a significant reduction in percentage recombination between Gl and Sb from fifteen to a level between five and ten in four out of six of the original lines. In most cases this reduction occurred rather rapidly after the initiation of the experiment. In the remaining two lines there was no significant decrease in recombination value; there was, however, a significant increase in at least one subline of this group. The rapid rate of change of recombination value is most readily explained by the presence of a recombination modifying gene which is linked to the modified region. Genetic random drift was again shown to have an important effect on changes in recombination value in small populations. High recombination was almost completely recessive to low recombination in the one case examined. Lethal genes were fixed in sheltered regions of unmarked third chromosomes in five lines or sublines. These results are discussed in relation to the mode of development of permanent heterozygosity in some species of plants.     

Naturally Occurring Enzyme Activity Variation in DROSOPHILA MELANOGASTER. II. Relationships among Enzymes

This report describes an investigation of the specificities of the genetic effects, caused by whole chromosome substitution, on the activities of 23 enzymes in Drosophila melanogaster. Two types of correlation estimates are examined, the product-moment correlation over the chromosome substitution line means and the corresponding correlation of line effects, which is a standardized covariance component estimate. The two types of correlations give very similar results. Although there is ample evidence for specific line effects on individual enzyme activities, there are extensive intercorrelations among many of the enzymes for both second- and third-chromosome substitution lines. The pattern of correlations with respect to the metabolic functions or other properties of the enzymes is difficult to visualize by inspection of the correlation matrix, so a multivariate graphical technique, the biplot (Gabriel 1971), was employed to obtain a two-dimensional view of relationships among the enzyme activities. The second and third chromosome lines show similar patterns. Four of the five mitochondrial enzymes form one highly intercorrelated group whereas another highly intercorrelated group contains several cytosolic enzymes. Within the cytosolic group, particularly high correlations are observed between enzymes that have glucose 6-phosphate as a substrate or product and between enzymes that are NADP-dependent. Although the pattern of intercorrelations is not clearly explicable in terms of metabolic relationships among the enzymes, there is some tendency for enzymes that catalyze sequential reactions or share a substrate or product to have correlated activity levels.     

Techniques for Manipulating Chromosomal Rearrangements and Their Application to DROSOPHILA MELANOGASTER. II. Translocations

Translocations have long been valued for their segregational properties. This paper extends the utility of translocations by considering recombinational derivatives of pairs of simple reciprocal translocations. Three major derivative structures are noted. One of these derivatives is suitable for use in half-tetrad experiments. A second should find use in recombining markers with translocation breakpoints. The third is an insertional-tandem duplication: it has a section of one chromosome inserted into a heterologue with a section of the latter chromosome tandemly repeated about the breaks of the insert. All of these structures are contained in "constellations" of chromosomes that regularly segregate aneuploid-1 products (informationally equivalent to nonrecombinant adjacent-1 segregants) for one of the parental translocations but do not segregate euploid products. This is in contrast to the parental T₁/T₂ constellations which segregate euploid products but not aneuploid-1 products. Methods are described for selecting translocation recombinants on the basis of this dichotomy. Several examples of translocation recombinants have been recovered with these techniques, and the recombination frequencies seem to be consistent with those observed for crossovers between inversion breakpoints. Recombinant chromosomes tend to disjoin, but it is observed that the tendency may vary according to the region involved in the recombination, and it is suggested that this difference reflects a difference in chiasmata terminalization times. Special consideration is given to insertional-tandem duplications. Large insertional-tandem duplications are useful in cytogenetic screens. Small insertional-tandem duplications are useful in gene dosage studies and other experiments that require an insert from one chromosome to another. Large duplications can be deleted to form small duplications. To generate a small insert for a specified region, it is only necessary to have one translocation with a breakpoint flanking the region of interest. The second translocation can have a breakpoint quite far from the region: an insertional-tandem duplication containing the region that has one closely flanking breakpoint can be deleted to create a smaller duplication that has two closely flanking breakpoints.     

Genetics of Parthenogenesis in DROSOPHILA MELANOGASTER. II. Characterization of a Gynogenetically Reproducing Strain

A strain of Drosophila melanogaster, named gyn-F9, can reproduce by gynogenesis. On mating with a male sterile mutant, ms( 3)K81, gyn-F9 females produced impaternate progeny at a rate of about 15 flies per female, which was almost 2000 times as frequent as that of the control. When the females were mated with normally fertile males, the number of offspring varied extremely from parent to parent, with average fertility being much lower than that of normal females. Nearly one-third of these bisexual progeny were either triploid females or intersexes. Among the rest of the progeny, some were diploid impaternates having developed without syngamy. The gynogenetic property of gyn-F9 is primarily governed by a few genes, most likely two recessive genes, one each located on the second and third chromosomes. The impaternates were found to restore their diploidy by the fusion of two nonsister nuclei out of the four egg pronuclei which result from the second meiotic division (central fusion). Although nondisjunction occurs frequently in the meiosis of gyn-F9, this is unlikely to bring about an appreciable number of diploid gametes developing into impaternates. Possible mechanisms of the evolutionary origin of parthenogenesis are discussed in relation to these findings.     

Estimation of Fitness Components in DROSOPHILA MELANOGASTER. II. Influence of Reduced Transmission Frequency

Results are presented of further analyses of the significant effects of reciprocal crosses reported by Katz and Cardellino (1978) in regard to viability indices of wild-type second chromosome heterozygotes. The observed differences between reciprocal crosses can be explained by the existence of reduced transmission frequencies of the wild-type homologue from Pm/+ and Cy/+ paternal parents. Mean estimates of transmission frequencies from Pm/+ and Cy/+ males in California and Japan populations are significantly less than the Mendelian expectation of 1/2. The transmission frequencies of +(i) chromosomes from Pm/+(i) and Cy/+(i) males are also found to be positively correlated in the California and pooled populations, suggesting that the degree of distortion is primarily due to the +(i) chromosome rather than to Cy or Pm. A sufficient estimator of relative viability that is independent of distorted transmission frequencies is derived for use in the Cy/Pm technique of viability estimation.     

干扰素在哺乳动物早期胚胎发育中的作用

干扰素是由多种细胞产生的可溶性糖蛋白,具有广泛的抗病毒、抗肿瘤和免疫调节作用.但是越来越多的实验结果表明干扰素在哺乳动物胚胎植入子宫、怀孕的维持以及早期胚胎发育中发挥着重要作用.结合本实验室的研究工作对干扰素的作用机制和近年来这一领域的研究进展做一综述.     

Changes in Acetylcholinesterase Molecular Forms During the Embryonic Development of Torpedo marmorata

Abstract: Multiple molecular forms of acetylcholinesterase from electric organ and electric lobe of Torpedo marmorata were examined at various developmental stages by sucrose density sedimentation. Four major forms were characterized by their apparent sedimentation coefficients of 6 S, 11 S, 13 S, and 17 S. Embryonic lobe possessed at early stages predominantly the 11 S form. With maturation the 17 S form became the most abundant. The early embryonic stages of the electric organ were characterized by predominating amounts of 6 S and 11 S forms. With differentiation of the postsynaptic membrane of the developing electrocytes, 13 S and 17 S forms replaced the slower-sedimenting forms. Concomitant with the formation of synaptic contacts, a transient increase in the 13 S form was followed by a dramatic accumulation of rapid-sedimenting 17 S form. The establishment of fully functional synapses was accompanied by an increase in the amount of the hydrophobic 6 S form. At birth, equal amounts of 6 S and 17 S form were found, with the other forms present in only trace amounts. The observed characteristic changes correlated with morphological and physiological events, indicating a close functional relationship between the accumulation of the 17 S form and synapse formation and the accumulation of the 6 S form and onset of function.