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Erythrocytes, which appeared to belong to a weak A subgroup, were studied by the indirect immunofluorescence technic utilizing anti-A typing serum and fluorescein-conjugated anti-IgG/IgM. Rare, single fluorescing cells, similar to Ax control cells, were observed in preparations of erythrocytes from three members of the family studied, the father and two sons. The mode of inheritance of the weak A (Aw) gene, presumably allelic at the ABO locus, was elucidated by direct observation of fluorescent patterns in erythrocytes of family members. This technic can be useful in detecting weak subgroups of the ABO blood group system. However, it is not possible to classify these weak subgroups into specific categories, e.g ., A3, Am, or Ax, using this technic, since they do not segregate into well-defined subgroups but show considerable degree of overlap. The fluorescent antibody technic, as opposed to the absorption and elution methods commonly used to identify weak subgroups, allows direct observation of the antigens present on erythrocytes. Furthermore, saliva studies used for identifying ABO subgroups can be employed only for those individuals who secrete soluble blood-group substances. Since the fluorescent antibody technic is not dependent on secretor status, it is valuable for investigating weak subgroups in these persons.

Nonmating mutants were also isolated from haploid strains of yeast of both mating types. The mutants were characterized with respect to their ability to produce and respond to specific yeast sex factors, their ability to mate at low frequencies, and the ability of the low-frequency diploids to sporulate. Loss of the ability to mate by either mating type was invariably accompanied by the loss of one or more, and in some cases, all, of the above capabilities. The results strongly indicate that the sex factors are functionally involved in the conjugation process.

A new type of host defective Escherichia coli mutant, hd590, is described. T4+ infection of this mutant results in (1) an abnormally low rate of T4 DNA synthesis that is constant throughout the latent period; (2) relatively low amounts of specific late T4 proteins; (3) the production of empty T4 heads, but not of tails or tail fibres. Two types of T4 mutants, one in T4 gene 31 and the other near T4 gene 39, overcome the hd590 block.

A Markov process (chain) of gene frequency change is derived for a geographically-structured model of a population. The population consists of colonies which are connected by migration. Selection operates in each colony independently. It is shown that there exists a stochastic clock that transforms the originally complicated process of gene frequency change to a random walk which is independent of the geographical structure of the population. The time parameter is a local random time that is dependent on the sample path. In fact, if the alleles are selectively neutral, the time parameter is exactly equal to the sum of the average local genetic variation appearing in the population, and otherwise they are approximately equal. The Kolmogorov forward and backward equations of the process are obtained. As a limit of large population size, a diffusion process is derived. The transition probabilities of the Markov chain and of the diffusion process are obtained explicitly. Certain quantities of biological interest are shown to be independent of the population structure. The quantities are the fixation probability of a mutant, the sum of the average local genetic variation and the variation summed over the generations in which the gene frequency in the whole population assumes a specified value.

A set of 64 mutants of Saccharomyces cerevisiae that confer sensitivity to X-ray inactivation were analyzed genetically to determine the number of genetic loci involved. The mode of interaction of various combinations of mutants was also determined. A minimum of 17 genes, when mutant, increase X-ray sensitivity of yeast, primarily by eliminating the resistance of budding haploid cells and by removing the shoulder on the survival curves of diploid cells. Eight mutant loci affect principally X-ray sensitivity while the remaining genes also control sensitivity to ultraviolet. Some of the genes when homozygous block sporulation or result in partial or complete sterility. Examination of the survival responses of multiple-mutant strains indicated a minimum of two pathways in the repair of X-ray damage. A number of the mutants have been mapped and these were found to be dispersed over the genome.

Synthesis of maltase in Saccharomyces cerevisiae is under the control of induction by maltose or some metabolic derivative of maltose and this induction is prevented during catabolite repression. Induction of maltase synthesis requires the presence of any one of several maltose genes. The function of one of these genes, MAL2, has been investigated by mutational analysis.

A survey of serum Pi, Cp, Hp and Tf was carried out in 104 Bengali Hindu Mahishya and 123 Bengali Muslim of West Bengal, India.

A new inherited variant of α1-antitrypsin (protease inhibitor or Pi) has been found in five individuals of a family of Welsh origin. The new allele is called PiN, as the α1AT product migrates in acid starch gel between the products of the PiM and PiP alleles. The individuals carrying the PiN allele are all of Pi type MN. The new variant has been compared in several electrophoretic systems with other variants migrating in a similar region by acid starch gel electrophoresis (M, P, S, V, W and X). Acid starch gel and crossed antigen-antibody electrophoresis are most suitable for distinguishing the PiN product. By immunofixation electrophoresis, N has a mobility only slightly different from that of M, however the value of this method can be seen for distinguishing other slow variants which cannot be clearly distinguished on acid starch gels. Twenty-three variants of α1AT are now known. Twenty-two of these are electrophoretic variants and one, the null allele (Pi−), produces no α1AT.

The frequencies of electrophoretically distinguishable allelic forms of enzymes may be very different from the corresponding frequencies of structurally distinct forms, because many sequence variants may have identical electrophoretic charge. In large populations such frequencies will be determined largely by the number of amino acid sites that are free to vary. The number of distinguishable electrophoretic variants will remain fairly small. Beyond some limiting size, no further effect of population size on allele frequencies is expected, so isolated large populations will have closely similar allele frequencies if polymorphism is due largely to mutation and drift. The most common electrophoretic alleles are expected to be flanked by the next most common, with the rarer alleles increasingly distal. Neither strong selection nor mutation/drift interpretations of enzyme polymorphism are yet disproven, nor is any point between these extremes.

In Escherichia coli wild-type cells, a mutation at the β-glucoside regulatory gene ( bglR + to bglR − ) leads to simultaneous expression of inducible phospho-β-glucosidase B ( bglB + ) and a β-glucoside-specific species of enzyme II (β-glucoside transport I [ bglC + ]); an additional mutation ( bglS + to bglS4 ) allows these enzymes to be formed constitutively. The bgl alleles have been mapped in the following order: pyrE, bglA, bglB, bglS, bglR, bglC, ilvD . The back mutation in the regulatory allele ( bglR − to bglR + ) caused the cessation of the expression of the bglB + , bglS + or bglS4, bglC + alleles. However, a mutation in a strain with bglB + , bglS4, bglR8, bglC + alleles, at the ini site that lies between the bglS4 and the bglR8 allele, allowed the expression of the bglS4 and bglB + alleles, but showed no affect on the expression of the bglC + allele. It is suggested that the ini mutation possesses a promotor-type function that in the absence of regulatory allele function ( bglR8 ) renews the functioning of only the bglS4 and bglB + alleles. The complementation studies have shown that the bglB + , bglS + or bglS4, bglC + alleles are expressed only in cis to the bglR − allele. In the constitutive strain ( bglB + , bglS4, bglR − , bglC + ), the expressed bglS4 allele formed a soluble product that acts in trans over the bglB + and bglC + alleles and that appears effective only when the bglB + and the bglC + alleles are expressed in cis to the bglR − allele. It thus showed that the constitutive biosynthesis of phospho-β-glucosidase B and β-glucoside transport I is under positive control. Since the regulatory allele bglR − lies between the bglS4 and the blgC + alleles, and acts in cis , it appears that the mutation ( bglR + to bglR − ) allows the initiation of transcription in one direction to express the bglS4, bglB + alleles and in the other to express the bglC + allele. The structural genes bglB and bglC lie adjacent to the regulatory genes bglR and bglS , and the structural genes are coordinately controlled by the regulatory genes. It is, therefore, proposed that the bglB, bglS, bglR, bglC genes form a bgl operon.

Mathematical formulae for the sampling variances of average heterozygosity and Nei's genetic distance are developed. These sampling variances are decomposed into their two components, i.e. the inter-locus and intra-locus variances. The relationship between the number of loci and the number of individuals per locus to be examined for estimating average heterozygosity and genetic distance is also discussed. The utility of the inter-locus variance of heterozygosity for studying the mechanism of maintenance of genetic variability in populations is indicated.

Summary The genetic effect of caffeine has been investigated in two different genetic regions of chromosome II of S. pombe , at different distances from the centromere. In all cases caffeine reduced the number of single and double crossing-over recombinants. The effect of caffeine was also studied on the frequency of gene conversion between heterozygous sites located at different intervals in the ade7 locus. The genc- conversion frequency was differently influenced by caffeine, depending on the distance of heteroalleles analyzed.

A rif r mutant of E. coli is described whose resistance to rifampicin depends on the composition of the growth medium and the recA allele.

Hairpin-tail (Thp) is a new allele of brachyury on chromosome 17 (linkage group IX) of the mouse. The morphological effects in the heterozygote are on the notochord and the tail. The homozygous abnormal is unknown. Thp is unique in that the phenotype of the heterozygote seems to depend on the source of the Thp gene. If it is inherited via the egg the phenotype is extreme and death follows in utero. Embryos derived from a Thp sperm and a+egg are less abnormal and viable. This is not a simple maternal effect, as Thp×Thp matings produce two distinct types of heterozygous embryos.

A temperature-sensitive lethal allele of suppressor of forked, l(1)su(f)(ts67g) (ts67), has been discovered and characterized as follows: Flies which are hemizygous for ts67 live at 18 degrees and 25 degrees but die at 30 degrees primarily as larvae. The temperature-sensitive period for ts67 homozygotes or hemizygotes begins in second instar and ends at pupation. ts67 is lethal at 30 degrees when heterozygous with suppressor of forked (su(f)), a deficiency for suppressor of forked (su(f)(-)), and a non-conditional lethal allele of suppressor of forked (3DES). It is viable at 30 degrees when heterozygous with the wild-type allele of suppressor of forked. At 25 degrees but not at 18 degrees forked bristles are suppressed in flies of the following genotypes: f(s)ts67/Y, f(s)ts67/f(s)ts67, f(s)ts67/f(s)su(f), f(u)ts67/f(s)3DES, f(u)ts67/f(s)su(f)(-), f(u)ts67/f(s)su(f). There is some suppression of forked bristles at 25 degrees in the heterozygote, f(s)ts67/f(s)+(su(f)). The forked bristle phenotype is not suppressed at either temperature in flies of the genotypes f(u)ts67/Y, f(u)ts67/f(u)ts67/ (f(s) and f(u) indicating suppressible and unsuppressible alleles of forked). The temperature-sensitive period for suppression of forked bristles begins at pupation and extends through the period of bristle synthesis. The deficiency phenotype (bristles reduced in size or absent, wing wrinkled or blistered, eyes rough) typical of flies of the genotype f(s)su(f)/f(s)su(f)(-) at 18 degrees and 25 degrees , is exhibited by flies of the genotypes f(s)ts67/f(s)su(f)(-) at 25 degrees and f(u)ts67/f(s)su(f) at 29 degrees . An allele of lozenge (lz(1)) which can be suppressed by su(f) is suppressed at 25 degrees but not at 18 degrees in lz(1)ts67/Y males. ts67 homozygous females are fertile at 25 degrees but sterile at 30 degrees . The hypothesis is discussed that the su(f) locus codes for a ribosomal protein and that suppression and enhancement are affected by mutations at the locus by mutant ribosome-induced misreading. The possibility is presented that ts67 may be used to determine the translation time in development of any gene.

l-Glycerol 3-phosphate dehydrogenase (E.C. 1.1.1.8) was purified from the muscle of BALB/cJ and C57BL/6J mice. The half-lives of the enzyme at 50 C were 6 and 33 min, respectively, for the BALB/cJ and C57BL/6J strains. Enzyme preparations from the two strains of mice were compared with respect to the following properties and found to be essentially indistinguishable: Km values for dihydroxyacetone phosphate, NADH, l-α-glycerophosphate, and NAD+; maximum velocity; competitive inhibition by inorganic phosphate; pH optimum; energy of activation; electrophoretic mobility; molecular weight and subunit molecular weight. From these data, it is concluded that the kinetic properties of the purified enzyme are not the factors responsible for the differences in activity found in crude homogenates of mouse tissues.

A total of 213 Kadar from a number of villages in the Anamalai Hills, South India have been tested for 4 blood group, 5 serum protein and 15 enzyme systems, as well as haemoglobin. The frequencies of genes in the ABO, MN and Rh blood group systems are compatible with values reported previouslythe fourth blood group system Ina was invariant, all persons tested being In(a-). Similarly no variants were detected in the transferrin, caeruloplasmin and albumin serum protein systerns. The haptoglobin gene Hp1 had a frequency of 0.41, high for Indian populations and also the Gm-1–2allele had a high frequency. Two individuals had the rare phenotype Gm (–1, +2). Amongst the red cell enzyme systems distinctive variants were detected in the phospho-gluconate dehydrogenase, phosphoglucomutase (locus 1) and peptidase B systems. The allele PGDKadar controls an electrophoretically fast variant and examples of combinations of this allele with PGDA, PGDC and itself were observed. In the PGM (locus 1) system an allele controlling a slower than normal component was present and may be identical with the PGD61 (African) allele detected in a black African. Individuals homozygous for this allele and others heterozygous with it and the normal PGM11and PGM12alleles were present. A single person with a peptidase B variant was detected. The mobility of the variant band was indistinguishable from the Pep B 6 in Australian aboriginals. The pb allele of the acid phosphatase system accounted for nearly 90%, Calcutta-1 variants had a frequency of 3.3%, the AK2 gene frequency was only 3.3%, and only two cases of HbS were detected. All other systems were invariant. Theories concerning the origin of the possible negrito-like traits in a small number of Kadar were discussed and the present evidence was considered to support the possibility of past African negro admixture on a small scale. The postulated genetic reconstruction of the ancestral Kadar population suggests that they may have been similar to Melanesian and Australian aboriginal populations, but that this original genetic structure has been modified through incorporating genetic elements not only from black Africans but from surrounding Dravidian populations.

Significant correlations between allelic frequencies and environmental variables in a number of insect species have been demonstrated by multivariate techniques. Since many environmental variables show a strong relationship to geographic location and since gene flow between populations can also produce patterns of gene frequencies which are related to the geographic location, both selection and gene-flow hypotheses are consistent with the observed correlations. The genetic variables can be corrected for geographic location and so for linear gene-flow patterns. If, after correction, the genetic variables still show significant correlations with similarly corrected environmental variables, then these correlations are consistent with hypotheses of selection but not of gene flow. The data of JOHNSON and SCHAFFER (1973) have been reanalyzed using the method of canonical correlation after correction for geographical location by means of multiple regression. Five of the nine loci studied exhibit significant canonical correlations. These results, under the assumption of linear gene flow, support hypotheses of selective action of environmental variables in the genotype-environment relationships observed.

A large body of family data was analyzed to explain the genetics of hypodontia. Two multiple threshold models that were developed for quasicontinuous traits were used. The data fit the polygenic model much better than they fit the single major gene model.

The mutant stock eyeless-ophthalmoptera of Drosophila melanogaster develops normally at 17°C, but the eye produces an outgrowth of wing tissue at 29°C. High temperature is effective in altering phenotype only if applied during the second instar. This demonstrates a genetically controlled developmental process acting during mid-larval life which determines whether cells of the optic imaginal disc embark upon a developmental pathway leading to wing or to eye.

Covariances between traits can be partitioned into additive and dominance genetic components and between- and within-family environmental components, using a method analogous to that used in the analysis of single traits. The problem arises as to whether all additive genetic components simply reflect a single additive component, in the sense that, given an appropriate rescaling of the breeding values, a single additive genetic component would adequately describe the additive genetic variation. The statistical procedure for testing this hypothesis is discussed in detail. Similar considerations apply to the dominance variation. The approach is applied to twin data given by Loehlin and Vandenberg (1968) on covariation between five of Thurstone's Primary Mental abilities. Although the data do not permit a reliable separation of additive and dominance components, it is shown that a single genetic component will account for almost all the genetic variation and covariation. Unless there is marked linkage disequilibrium, this implies that most of the genetic variation for the five traits can be attributed to the pleiotropic action of genes at a common set of loci.

A unified biochemical and genetic study has led to the location of the gene for erythromycin resistance in 4 mutants of Chalamydomonas reinhardi and the identification of the chloroplast ribosomal protein altered in these strains. Tetrad analyses of crosses involving the Mendelian mutants ery-M1a, ery-M1b, ery-M1c, and ery-M1d indicate that they are closely-linked alleles which map to nuclear linkage group XI. The proteins of the 52s subunits of wild-type and the 4 ery-M1 mutants were compared by one-and two-dimensional gel electrophoresis. Protein LC6 from wild-type differs in net charge at pH 5 from the homologous component found in each of the mutants. The LC6 in ery-M1b is also 30% smaller in molecular weight than the wild-type protein. The variety of altered forms of LC6 observed and the allelic nature of the genetic determinants strongly support the view that the nuclear locus for erythromycin resistance of the ery-M1 group is the structural gene for the chloroplast ribosomal protein LC6.

We have found that the phenol oxidase activity in 50-hr Drosophila melanogaster pupae is much greater than that of adult flies. The mutants lz and lzg have all of the phenol oxidase components present in wild type, whereas the mutant tyr-1 has all of the wild-type components but the activity of each component is greatly reduced in comparison with wild-type activity. The newly discovered lozenge allele, lzrfg, lacks all phenol oxidase activity.

A mutation at the divD locus in Salmonella typhimurium confers a round-cell morphology and enhances cell division under certain growth conditions.

The pleiotropic effects of six radiation-induced lethal alleles at the albino locus in the mouse include deficiencies of various enzymes and of serum proteins. Closely correlated with the biochemical deficiencies are severe ultrastructural abnormalities of endoplasmic reticulum membranes and the Golgi apparatus in liver and kidney cells. Complementation studies led to the distinction of four different complementation groups among the six lethal alleles. The results are compatible with the interpretation that the six lethal alleles represent overlapping deletions of various sizes at and around the albino locus in the mouse, in a region concerned with the control of biochemical and structural differentiation.

Females of the parasitic wasp, Nasonia vitripennis Walker, were generally nonreceptive after the initial copulation. But if they were inseminated twice, once by each of two virgin males in quick succession, they seldom retained for utilization any sperm from the second mate. If both males, or first males only, were partially depleted of sperm by prior copulations, then sperm from both males were often retained and utilized daily throughout a two- to three-week laying period. Sperm mixing resulted in random usage or in initiai preferential usage from either the first or second male. Precedence in usage of sperm from one mutant (oy) is suggested. When groups of males competed for females, some of the females were not inseminated and some others were doubly inseminated.

Of 43 non-complementing alleles studied of the Saccharomyces cerevisiae fatty acid synthetase locus fas 1, 27 are reverted by external suppressors whereas 16 are susceptible only to intragenic suppression. Of the externally suppressible mutants 12 are reverted by both, amber and ochre suppressors, another 12 only by amber suppressors, and 3 are not suppressed by either of them. According to their response to the acridine mustard, ICR-191, one of the mutants not suppressible by external suppressors appears to be a frameshift mutation, whereas the others are suggested to be missense mutations. By X-ray induced mitotic recombination a genetic fine structure map of the complementing as well as of the noncomplementing fas 1-alleles was constructed. It was found that the alleles of the non-pleiotropic complementation groups II, Va, Vb and Vc map at distinct and characteristic regions within fas 1, each of them covering 9.8, 13.5, 5.3 and 1.6 X-ray map units, respectively. On the other hand, the non-complementing fas 1-alleles are distributed randomly over the entire locus, no matter whether they were nonsense or missense mutations. These non-complementing alleles are spread over a DNA region of 72 X-ray map units length and all the complementing alleles studied map within this region. These results suggest that fas 1 encodes only one, functionally complex, polypeptide chain.

The ilv 1 gene of Saccharomyces cerevisiae contains functions associated with both structural and regulatory genes and therefore is termed a multifunctional gene. The ilv 1 gene product catalyses the first step in isoleucine biosynthesis and is involved in repression of the isoleucine-valine pathway. The intracistronic discrimination of the two functions is presented.

Wild type and 22 mutant strains of Neurospora crassa were compared for L-glutamine: D-fructose 6-phosphate amidotransferase (GFAT: EC 2.6.1.16) specific activity. The mutant genes map at eleven functionally nonallelic loci, mutations at which result in altered mycelial and ascus morphologies. The enzyme GFAT, which is involved in the synthesis of the important mycelial wall constituent chitin, was investigated as a possible causal factor in determining the altered morphologies. When compared with the wild-type (control) activity, a statistically increased GFAT activity was detected in crude extracts of six mutant strains. Two of these strains carry mutant alleles mapping at the peak locus (peak-2 and clock) and the remaining four carry mutant genes mapping at four other loci. GFAT activity was not significantly different from that of wild type in crude extracts prepared from nine other strains carrying mutant alleles that map at the peak locus, or from seven strains carrying the remaining mutant alleles mapping at other loci. In the two cases tested, including that of peak-2, the activity increase segregated with the mutant morphological phenotype when cultures derived from ascospores of tetrads isolated from crosses of the mutants with wild type were assayed.

The two common melanic forms of the Pale Brindled Beauty Moth, Phigalia pilosaria (pedaria), in Britain are controlled by a pair of alleles. Dominance is complete and is in order of darkness; monacharia the extreme, unpatterned melanic is dominant to a patterned melanic, termed “intermediate”, which is in turn dominant to the typical, non-melanic form. The two alleles control the coloration of the wings and the body of the male, and the body of the brachypterous female. Dilute individuals, where all the darker pigment is replaced by a golden yellow, occur in both melanic forms and typical. Such insects are homozygous for a dilute allele, recessive in effect, at a locus unlinked to monacharia.

This paper gives a proof that certain quantities are independent of the geographical structure of a population. The quantities are: (1) the fixation probability of a mutant; (2) the sum of the quantity x(1 − x), where x is the mutant frequency, while the mutant is segregating; and (3) the quantity x(1 − x) summed over the generations during which the gene frequency in the whole population assumes a specified value. The independence of geographical structure for the latter two quantities is not exact if there is selection, but is a close approximation. The model is a geographically structured version of Moran's haploid overlapping generation model. The population consists of colonies connected genetically by migration. Each individual has the same negative exponential lifetime distribution. When an individual dies, it is immediately replaced by an individual born in the same colony with a probability proportional to the frequency and fitness of the type giving birth. In a diploid population the quantity x(1 − x) is proportional to the heterozygosity.

The hyperkinetic mutants, Hk 1 and Hk 2 , jump and fall over when an object moves near them. This behavior, the kinetogenic response, has been measured by the experimenter moving his hand above a vial containing a single fly and scoring the number of positive responses in fifty trials. The response is higher in Hk 1 than in Hk 2 and has remained so over a period of several years and in different genetic backgrounds. The Hk 1 /Hk 2 heterozygote also responds to movements, establishing the allelism of the two mutants.—When Sh 5 , a shaker mutant at another locus on the X chromosome, is introduced into the same chromosome as Hk 1 or Hk 2 , the response is reduced in proportion to the number of Sh 5 mutant genes added.—When Hk 1 or Hk 2 is heterozygous with a deficiency for the hyperkinetic region of the X chromosome, the expression is more abnormal than the respective Hk 1 or Hk 2 homozygote. This shows that the mutant genes are producing an altered gene product, or less of the normal, since one mutant gene by itself has a more abnormal expression than two. A tentative explanation has been offered for the observed mutant behaviors.

The basis for the specific pattern of ultraviolet-induced reversion of cyc1-9, an ochre allele of the structural gene for iso-1-cytochrome c, has been examined in radiation-sensitive strains of yeast. Previous analysis, using RAD+ strains, showed that 21 out of 23 cyc1-9 revertants induced by ultraviolet light arose by A · T to G · C transition at the first position in the UAA codon, the remaining two occurring by A · T to T · A transversion at the second position (Stewart et al., 1972; Sherman & Stewart, 1974). All possible base-pair substitutions could be obtained with the aid of other mutagens. It has now been shown that this specificity depends largely on the action of the RAD6 locus, since ultraviolet-induced revertants of cyc1-9 arose by a variety of base-pair substitutions in a strain carrying the rad6-1 allele. Induced reversion frequencies in strains carrying this allele are much lower than normal, though significantly higher than the spontaneous frequency, and the strains are more sensitive to the lethal effects of both ultraviolet and X-irradiation. The phenotypically similar rad18-2 mutation, which appears to block the same repair pathway as rad6-1, also has some effect on the reversion specificity, but its action depends on the presence of other, unidentified, mutations. Specificity was, however, completely unaltered in an excision-defective strain carrying the rad1-2 allele. Induced reversion frequency of cyc1-9 was much higher than normal in this strain. Photoreactivation studies indicated that pyrimidine dimers were responsible for most of the revertants in RAD+, rad1 and rad6 strains. These experiments show that the RAD6+ locus is intimately concerned with error-prone repair, and suggest that excision repair is substantially error-free.

Large changes in genotypic frequencies have been observed over a 2-year period in a population of Daphnia magna polymorphic for two alleles of malate dehydrogenase. These changes were not the result of migration or random drift. Genotypic differences in both parthogenetic and sexual egg production were observed. There was a strong correlation between the parthogenetic fecundities of the genotypes and their frequencies 1 month later. Sexual egg production was enhanced among low fitness genotypes. These observations strongly suggest that populations of Daphnia magna consist of a limited number of ecologically differentiated clones.

A trispeciflc anti-Ag serum (M. H.) was found to reveal a new Ag factor: Ag(i). Ag(i) occurs in 98.3% of the white population and is antithetical to Ag(h). The results of Ag(i) typing in Swiss, Tibetans and Senegalese are amalgamated with previously obtained genetic data. Different models for the Ag chromosome are discussed.

Diploid strains of Saccharomyces cerevisiae homozygous for mating type and capable of sporulation have been isolated. Tetraploid inheritance studies suggest that the ability to sporulate is controlled by a recessive gene unlinked to the mating type locus. The symbol sca (” sporulation capable”) has been assigned to this gene.