As the first step in a study of the effects of linkage and epistasis on equilibrium frequencies of lethal genes, the necessary and sufficient conditions for stable equilibria of two interacting recessive lethals are worked out on the assumption of linkage equilibrium. The condition necessary for linkage equilibrium to be maintained permanently is also examined. The genetic variance in an equilibrium population is shown to be composed only of the dominance and dominance×dominance compoments.

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(1) The effects of linkage and epistasis on the equilibrium frequencies of lethal genes were studied by numerical means, making use of an electronic computer. The changes in gamete and gene frequencies, linkage disequilibrium, and population fitness under selection were also examined. The selective values of A₁A₁B₁B₁, A₁A₂B₁B₁, A₁A₁B₁B₂, and A₁A₂B₁B₂ are denoted by a, b, c, and d respectively, those of the remaining genotypes being all 0, where A₂ and B₂ represent lethal genes.
(2) If a=b=c=d, there are no stable equilibria for two lethal genes even if there is linkage disequilibrium. If a is smaller than b and c or both, there occur non-trivial equilibria for the two genes jointly. The equilibium frequencies of lethal genes increases the recombination value between the two loci decreases, unless ad-bc=0 and the original population is in linkage equilibrium. If ad-bc=0 and the original population is not in linkage equilibrium the equilibrium gene frequencies depend on the sign of the original linkage disequilibrium as well as the recombination value. It does not appear that the initial gene frequencies affect the equilibrium values.
(3) Gene frequencies do not necessarily approach the equilibrium values straightly but in some situations the lethal gene frequencies first increase considerably and then begin to decrease, depending on the initial gamete frequencies. If the recombination value is large, the rate of change in gene frequencies is usually larger in early generations than in later generations, but if the recombination value is small, there occur situations where little changes of gene frequencies are observed in early generations.
(4) The equilibrium value of linkage disequilibrium has the same sign as that of ad-bc, if ad-bc≠0. If ad-bc=0, the sign of the equilibrium value conforms to the sign of the original linkage disequilibrium. The equilibrium values of linkage disequilibrium increases as linkage becomes tight for a given set of selective values. The forms of changes in gamete frequencies and linkage disequilibrium are again affected considerably by the recombination value and initial gamete frequencies.
(5) In some situations the population fitness decreases appreciably. This decrease is usually associated with the breakdown of linkage disequilibrium, but not always so.
(6) It has been indicated that the frequency of lethal chromosomes and the allelic rate of lethal genes are differentially affected by linkage disequilibrium. The effect of linkage on the genetic load manifested under inbreeding is also discussed. Further, the applicability of the results obtained to the artificial selection for quantitative characters is pointed out.

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This paper describes some genetical results on the acid-phosphatase type of larval blood in the silkworm. Five fundamental types of acid-phosphatase have been found in the various strains investigated. The acid-phosphatase isozymes are under the control of codominant allelic genes, Bph^O, Bph^A, Bph^B, Bph^C and Bph^D, and they show different migration rates in agar-gel electrophoresis.

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Evidences indicate that a man, doubly hemizygous for the abnormal genes of both series of color-blindness, manifests anomaly either of the protan- or the deutan-type. A method for estimating recombination value between the loci for the two color-blindness genes has been devised by modifying Smith's method for linkage test based upon Bayes' theorem, and z(θ) scores for various values of family size and recombination fraction are presented.
Families usable for such study should have (1) a phenotypically normal mother, (2) three or more boys examined for color vision of whom (3) at least one shows the protan-type anomaly and another the deutan-type anomaly.
Calculation based on 6 suitable pedigrees has yielded that the recombination value, at which the probability obtaining such a sample is highest, is about 0.06 under the assumption that the deutan type anomaly is epistatic over the protan type anomaly and about 0.15 if it is assumed that the protan type is epistatic over the deutan type.

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Some cytopathic changes in L cells infected with the HA⁺ and HA^- viruses and with mixture of both viruses were examined. The following results were obtained.
(1) The HA⁺ virus produced cell clumping and hemadsorption of fowl red blood cells around the infected cells, whereas the HA^- virus produced polynucleated giant cells without hemadsorption.
(2) The production of hemagglutinin in cells infected with the HA⁺ virus first became appreciable 10 hours after infection and a parallelism was found between the growth of virus and the production of hemagglutinin. The cells infected with the heat and UV-treated HA⁺ virus showed no hemagglutinin production. Inhibition of the production of hemagglutinin by actinomycin and puromycin indicates that viral DNA-dependent RNA and protein synthesis are indispensable for the production of hemagglutinin.
(3) The HA⁺ virus produced cell clumping whereas the HA^- virus produced polynucleated giant cells 6 hours after infection and their formation depended on multiplicity of viruses. The formation of polynucleated giant cells was not affected by mitomycin C and actinomycin but inhibited by puromycin. Although the heat-treated viruses produced no morphological changes in their host cells, the UV-irradiated HA⁺ and HA^- viruses produced cell clumping and polynucleated giant cells respectively.
(4) The fact that dual infection with both HA⁺ and HA^- viruses produced cell clumping but no polynucleated giant cells indicates that the changes produced by the HA⁺ virus were dominant.

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The present article deals with some cytological investigations on the effects of PCMB, BAL, alone or in combination, Isomytal, sodium azide and Tween 20 upon HeLa cells.
The application of PCMB or BAL induced in HeLa cells prompt and severe cellular damage, similar in pattern in both agents. Characteristic damages here induced were represented by stickiness, agglutination and irregular scattering of chromosomes at metaphase and anaphase-bridge formation. The action of both PCMB and BAL on interphase cells were rather slow, showing remarkable vacuolation of the cytoplasm and the appearance of granules stained red with MGG in the nucleus. They underwent pycnotic degeneration.
It was supposed that the cellular damage caused by PCMB would be attributable to the inactivation of enzymes through the blockade of the active thiol groups. Cellular damage by BAL on cells seemed to be due to its powerful reducing activity.
The combined application of PCMB (0.05mg/ml) and BAL (0.001mg/ml) on the HeLa cells produced less obvious cellular damage. This seemed to indicate that PCMB and BAL reacted competitively one another.
Isomytal, sodium azide and Tween 20 affected cells at interphase as well as those in the course of mitosis, especially damage at metaphase being striking.

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Chromosomes were studied in regenerating cells derived from 5 partially hepatectomized rats weighing 240 to 360g. Several previous investigators have reported that polyploid cells occurred in the regenerating rat liver at more than 40% of metaphase cells in cell population (Biesele 1944, Makino and Tanaka 1953, Gläss 1958). However, the frequency of the polyploid cells in the present study were found to be substantially lower than the reported cases by the previous workers; it was only 11.2% on an average ranging from 22 to 3 per cent. Aneuploid cells were also very few in number, and most of the cells observed had a normal diploid number of the rat (2n, 42).
Detailed karyotype analyses were made on well-spread metaphase cells taken from the regenerating liver and supplementally on those from the normal embryonic liver grown in vitro. The results showed that all of the diploid cells analyzed had a normal chromosome constitution of the rat. Two representative karyotypes were shown in Figs. 1 and 2. As shown in the figures, the chromosomes can be classified into 5 different autosomal groups (I-V) and the sex elements. The X chromosome was recognized as one of the acrocentrics which ranks between the 3rd and 4th autosomal pairs. The Y chromosome was identified in the male complement to the smallest acrocentric element approximately corresponding in size to the 17th autosomal pair. The results of the karyotype analyses are in general agreement with those reported by Tjio and Levan (1956), Makino (1957) and particularly by Hungerford and Nowell (1963).

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Four curculionid weevil species belonging to the subfamily Brachyrhininae collected in Sault Ste. Marie, Ontario, Canada, were studied cytologically. No males were found in every species here studied. The results are summarized in Table 1.
Table 1. Species of weevils under study and their chromosome numbers established
It was found that Brachyrhinus ovatus, Sciaphilus asperatus, and Trachyphloeus bifoveolatus had 33 chromosomes, while Tropiphorus terricola possessed 44 chromosomes. On the basis of the fact that the basic number of parthenogenetic weevils (Curculionidae) was reported as 11, the former three species is triploid and the latter species is tetraploid. In the light of the present results, it seems to be very probable that four species dealt with in this paper are parthenogenetic in reproduction.

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