The mitotic and meiotic chromosomes of Phagocata vivida were observed by the air drying method in the neoblasts of regenerating pieces and primary spermatocytes and oocytes, respectively. The chromosome number of this species was determined as 2n=36 or 36+1 B in somatic cells and n=18 or 18+1 B in germ cells. The karyotype consisted of 8 pairs of metacentric chromosomes and 10 pairs of submetacentric chromosomes. Chromosome No. 11 had a satellite at the end of the long arm. The karyotype of this species distinctly differed from those of four Japanese species; Ph. teshirogii, Ph. Kawakatsui, Ph. Papillifera and Ph. Suginoi, although it was common to all the five Phagocata species that chromosome No. 1 was extremely large and metacentric.
In order to estimate chromosomal homology between Aegilopsspeltoides (genomic constitution SS) and the tetraploid wheats (AABB or AAGG), effects of the B-chromosomes and genotypes of Ae. speltoides on chromosome pairing at MI of meiosis in F1 hybrids of Ae. speltoides × tetraploid wheats were investigated. In hybrids with B's, chromosome pairing was strikingly affected by the B's and very small amount of pairing was observed. In hybrids without B's, however, extensive pairing was observed, although the amount of pairing varied due to the speltoides genotypes involved. In these hybrids with or without B's, although some minor yet distinctive differences in pairing attributable to the kind of genomic constitution of the wheat parent were observed in the multivalent frequency and in the distribution (or terminalization) of chiasmata, both hybrids with different genomic constitution (SAB or SAG) had essentially the same amount of pairing. Since the B-chromosomes used did not cause asynapsis (or desynapsis) of homologous chromosomes in Ae. speltoides, the pairing reduced by the presence of B's in the hybrids does not seem to be homologous and is probably homoeologous. Therefore, it can be concluded that there is little chromosomal homology between Ae. speltoides and both tetraploid wheats of genomic constitution AABB and AAGG.
Parental characteristics in the hybrid progeny of the two rice species were observed in B2F1 plants and B2F6 (including a few B1F6) lines obtained from backcrosses between a sativa and a glaberrima strain. The backcross derivatives had different coefficients of relationship to glaberrima (or to sativa) parent ranging from 1/8 to 7/8. Ligule length, regenerating ability of excised stem segments, and various other characters were recorded. The measurement of a plant, i, for a character was evaluated by xi=(Xi-μ)/d, where μ=1/2(Xs+Xg), the mid-parent value, d=1/2(Xs-Xg), and Xs and Xg are the parental sativa and glaberrima values, respectively. The distribution of x values showed appreciable transgressiveness (overlap) in panicle axis diameter and three other characters, particularly in the B2F6 population, presumably as a result of gene recombination. Awn length also served as a measure of gene recombination since both parents were awnless. The standard deviation of x values for different characters was used as an index showing recombination of parental characteristics or “character discordance”. These data suggested that parental genes could be recombined almost freely. In ligule length and some other characters, however, B2F6 lines showing parental values (xs=1; xg=-1) were larger in number than those showing intermediate values, and the lines showing intermediate values tended to have a low productivity. Awn length was inversely correlated with seed productivity. Further, between two independent gene loci, a tendency toward restricted recombination was detected. These facts were considered as indications of so-called M-V linkage. Among the characters investigated, the probability of misclassification between the two species, estimated from intra- and inter-specific variations, was correlated with transgressiveness in the hybrid. Ligule length and secondary branch number per primary branch, which seemed to be useful as key characters, were practically non-transgressive and were subjected to M-V linkage more obviously than other characters.
The effects of inhibition of protein synthesis by puromycin on the replication of satellite DNA in the Kangaroo rat cells, D. ordii were studied. In all experiments, cells were partially synchronized at the beginning of the S phase. When protein synthesis is inhibited by puromycin, overall rate of DNA synthesis in the S phase cells is reduced. Replication of satellite DNA which replicates later in the S phase is equally sensitive to puromycin as early replicating other bulk of DNA. The reduction in the overall rate of DNA synthesis was further examined at the level of replicons by using DNA fiber autoradiography. The rate of DNA chain elongation within individual replicons is slightly reduced in puromycin-treated cells. However, this reduction in the rate of DNA chain elongation at the level of replicons does not entirely account for the inhibition of overall rate of DNA synthesis per cell. When cells were labeled for longer periods in the presence of puromycin, the formation of long radioactive pieces of DNA was prevented and small pieces were accumulated. The failure in the formation of long radioactive pieces may be due to the inability to activate replicons or their clusters which are not yet activated. These results indicate that inhibition of satellite DNA replication does require protein synthesis in similar manner as observed in the other bulk of nuclear DNA.
To gain further insight into the mechanisms of induction of dominant lethal mutations, the relationship between the chromosome aberrations in male pronuclei and unscheduled DNA synthesis (UDS) in spermatogenesis during 42 days after treatment with MMS was examined. Nine-week-old hybrid mice (C57BL/6J×DBA/2) were used in all experiments. For the detection of chromosome aberrations in first-cleavage metaphases, chromosome preparations were made by a new technique. UDS in male germ cells was detected by Sega's procedures (Sega et al. 1974). The frequency of eggs with one or more chromosome aberrations at the first-cleavage metaphase showed a close correlation with the high frequency of dominant lethals during 1 to 14 days after treatment. In particular, eggs recovered during 7 to 10 days were found to have more than 8 chromosome aberrations per egg. The types of structural aberrations observed were predominantly chromosome-types including fragments and dicentrics. The development of 3-day eggs obtained from females mated 7-10 days after treatment of the male mice with MMS was markedly delayed, with degenerated blastomeres and micronuclei. However, unfertilized eggs were not observed in this period. These results show that even sperm with MMS-induced lesions is capable of fertilization. On the other hand, UDS was detected during 16 to 24 days after treatment, with a peak at 20 days. Consequently, an opposite correlation was observed between UDS and dominant lethals induced by MMS in spermatogenic stages. These results suggest that chromosome damage induced from late spermatids to spermatozoa, where UDS was not observed, may produce chromosome aberrations in male pronuclei; these fertilized eggs with chromosome aberrations would show dominant lethal mutations resulting from early cleavage death.
A regulatory gene for transport systems of branched-chain amino acids, gleR, is closely linked to brnQ located at 8 units of the linkage map of Salmonella typhimurium. Co-transduction frequency for the region gleR-brnQ ranged from 92 to 96%.
A mutant mouse with small eyes was found in the breeding process for establishment of a new strain. The abnormality of the eye was discernible after birth, which was characterized by the lens obsolescence. The eyeball was reduced in size, although the ocular structures were well formed except for the lens. Mating experiments proved that the abnormality depends on a new autosomal dominant gene, Elo on chromosome 1.
A method for isolation of the nuclei from embryo of dormant barley seed is described. In them, metaphasic chromosome figures were found, and somatic association of metaphasic chromosomes was repeatedly observed.