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Ethanol intake by inbred and hybrid mice generally decreased after maturity, than increased in old age and senescence. Genetic differences in ethanol selection decreased with increasing age.
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Mating studies on individual couples of Drosophila melanogaster allowed the structure of inbred populations in terms of egg hatchability and egg-to-adult survival to be elucidated. The comparison between inbred (from brother-sister matings) and control (randomly crossed) populations distinguished between couples sensitive and insensitive to inbreeding. Mendelian ratios were observed for this "phenotypic trait" in the progeny of single couples. These ratios and a double mating experiment indicated that a gene or gene complex implicated in morphogenetic events blocked development during embryonic and larvo-pupal stages. The expression of this lethal gene in homozygous embryos depended on the genetic makeup of both parental flies, i.e., on male and female factors which act as regulatory components. Homozygous embryos which survived the first critical phase (from fertilization to hatching) continued to develop normally until the larvo-pupal period, when they died. Lethality was also modulated by the cytoplasmic composition of the parental eggs, as shown by taxonomic analysis and the double mating experiment. The results account for lethality throughout development due to inbreeding. They lead to an estimated genetic load from laying to adult stage of one "lethal equivalent".
Recombination fractions among four chromosome 3 enzyme loci were measured over a 20 generation period in experimental populations of Drosophila melanogaster. The experimental populations were initiated with complete pairwise linkage disequilibria among the marker loci, thereby providing an initial structure favorable to selection for recombination modification. The recombination data show no evidence of directional changes in recombination rates among the marker loci, although variation in estimates, both between families within generations and between generations was large. These materials also yielded much lower estimates for recombination fractions for the centromeric region of the third chromosome than previously reported. Taken in total, the experimental results show no evidence for recombination modification, although the results do indicate ample genetic variance for recombination rates.
The phenotypic arrays for seven erythrocyte antigenic systems of a sample of the Melbourne population were found to be distributed according to Zipf's Law. A simple model of heterozygote selective advantage was unable to account for the excess of observed frequencies of arrays over those expected under the random-mating hypothesis. Persons with (ccDEe, MMss) were over-represented and those with (A1, MNSs P1--) were under-represented in the sample.
The dynamical behavior of chromosomal segments undergoing strong selection was investigated in four replicate populations of Drosophila melanogaster. This was accomplished by following the joint behavior of allozyme markers at the loci phosphoglucomutase and esterase C, adjacent to the recessive lethal locus Glued, during and following the course of selection against Glued. The results show strong selection at other loci in the region of the marked segment. Examination of the joint dynamic of the two markers indicates that there must be more than one, and probably several, selected loci in the region under observation, with large epistatic effects. The mode of selection on the segment often results in excess heterozygosity at the markers, but does not appear to be constant in time. It is concluded that the density of selective effects in the region under study is substantial.
A two-locus model with three alleles at one locus and two at the other is studied. The viability system is such that all double heterozygotes have fitness unity, all single heterozygotes have fitness w smaller than 1 and all double homozygotes have fitness w-2. The following are the major findings: 1. There are more stable equilibria for tight linkage than in the corresponding three-locus model, even though the number of chromosomes is lower. 2. The equilibria stable for tight linkage do not belong to a unique high complementarity class, as is the case for two alleles at each locus. Instead the strength of selection determines the structure of the equilibrium. 3. The increase in number of alleles seems to reduce the possible extent of association between the loci. 4. The measure of this association is not well defined, although we have suggested a statistically standard way of getting over this. 5. A mutation introduced while a population is in linkage disequilibrium may, per medium only of the change in number of alleles, destroy the linkage disequilibrium.
Four replicate populations of Drosophila melanogaster, two reared on medium supplemented with ethanol and two reared on standard medium, were electrophoretically monitored for 28 generations. During the first 12 generations, allelic, genotypic and gametic frequencies were determined for eight polymorphic enzymes: GOT, alpha-GPDH, MDH, ADH, TO, E6, Ec and ODH. Samples from generation 18 and 28 were electrophoretically typed for ADH and alpha-GPDH. In addition, samples from generation 27 were analyzed for the presence of inversion heterozygotes. The experimental results showed rapid gene-frequency divergence between control and treatment populations at the Adh locus in a direction consistent with the activity hierarchy of Adh genotypes. Gene-frequency divergence between control and treatment populations also occurred at the alpha-Gpdh locus, although the agreement among replicates appeared to have broken down by generation 28. No differential gene-frequency change occurred at any of the six remaining marker loci. Furthermore, values of linkage disequilibria among all linked pairs of genes were initially small and remained small throughout the course of the experiment. Taking these facts into account, it is argued that the gene-frequency response observed at ADH is most probably caused by selection at the Adh locus. The gene frequency response at alpha-Gpdh can also be be accounted for in terms of the effect of ethanol on energy metabolism, although other explanations cannot be excluded.
Pyruvate kinase (ATP: pyruvate 2-O-phosphotransferase, EC 2.7.1.40) from human liver and red cells has been purified to homogeneity; its subunit structure and some of its kinetic characteristics have been studied. The influence of a partial proteolysis by trypsin on the subunit structure, the isozymic pattern and the kinetic characteristics of red cell and liver enzyme have been investigated. From the results of this study we may conclude that: 1. Liver (L-type) pyruvate kinase is composed of 4 identical L subunits while the major form of erythrocyte enzyme (PK-R2) is a heterotetramer designated as L2L2', the molecular weight of L' being slightly higher than that of L subunits (63 000 and 58 000 respectively). Pyruvate kinase PK-R1, predominant in the erythroblasts and the young red cells, is composed of four identical L' subunits. 2. A mild tryptic attack is able to transform PK-R1 into PK-R2, then PK-R2 into pyruvate kinase L (PK-L). The same proteolytic treatment transforms the L' subunits into L ones. 3. Consequently L-type pyruvate kinase seems to be initially synthesized in the erythroid precursors as an L4' enzyme secondarily partially proteolysed into L2L2'. In liver a very active proteolytic system would be responsible for the total transformation into L4 pyruvate kinase. 4. L4' enzyme exhibits Michaelis-Menten kinetic behaviour with an apparent Michaelis constant of 3.8 mM whereas L4 enzyme shows both positive and negative homotropic interactions towards phosphoenolpyruvate and has [S] 0.5 of 1.2 mM. The characteristics of L2L2' are roughly intermediate between those of L4' and of L4. Fructose 1,6-biphosphate decreases [S]0.5 for these three pyruvate kinase forms without suppressing the differences in the apparent affinity for phosphoenolpyruvate of these enzymes. 5. L4 pyruvate kinase is more inhibited by Mg-ATP than L4', with L2L2' in the intermediate range. 6. Tryptic treatment of each enzyme form studied transforms its kinetic behaviour into that observed for L4.
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A method has been devised to test intergenic complementation of mutations in the mitochondrial DNA of Saccharomyces cerevisiae. The test is based on the observation that diploids issued from pairwise crosses of certain mit- mutants with deficiencies in cytochrome oxidase, or coenzyme QH2-cytochrome c reductase, acquire high levels of respiratory activity shortly after zygote formation. Under our experimental conditions neither biochemical complementation, interallelic complementation, nor recombination has been found to contribute to any significant extent toward the respiration measured in the diploids at early times. The test has been used to study the number of complementation groups represented by a large number of mit- mutants. Results of pairwise crosses of mutants in the oxi 1, oxi 2, oxi 3, cob 1, and cob 2 loci indicate that complementation occurs between the oxi and cob loci between different oxi loci but not between the two cob loci. The five loci have, therefore, been assigned to four different complementation groups.
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Genetic experiments involving selected strains as well as single gene mutations have provided information concerning the organization of the Drosophila circadian system. The phase of the emergence rhythm of D. pseudoobscura can be altered by genetic selection without significantly affecting the phase and period of the light-sensitive pacemaker. The period of the D. melanogaster pacemaker, over the range 19 hours to 29 hours, can be encoded in the DNA sequence of a single genetic locus. The short-period and long-period mutations do not eliminate the pacemaker's temperature compensation mechanism. The short-period mutation alters the resetting behavior of the pacemaker from weak (type 1) in wild-type to strong (type 0) in the mutant. Five aperiodic mutations isolated in D. pseudoobscura belong to two complementation groups. In complements bearing one mutation from each group, the periodicity of the pacemaker is wild-type, but the phase of the emergence rhythm is 5 hours later than wild-type. Thus mutations in particular genetic loci have dramatic effects on the basic properties of circadian pacemakers and rhythms.