Multicopied DNA sequences with homology to the complete 2.9kb P element from a P strain in the USA were detected in nine natural strains (two P strains, three Q strains, four M strains) of Drosophila melanogaste from Japan and one (M strain) from Korea. Southern hybridization patterns with pπ25.1, which contains the complete P element, showed highly polymorphic distribution of P elements in genomic DNAs from these strains. Nevertheless, all these natural strains including strong M strains had a similar number i.e., about 50 copies of P elements per genome. However, the number of central-portion-retaining P elements surveyed by hybridization to PstI fragment from pπ25.1 was not similar in these strains; it was 25 for a fairly strong P strain, 16 for a weak P strain and 16-14 for two Q strains, but only 1 to 9 for five strains (Q, weak M, strong M) from a small island (Chichi Jima) and 8 for a weak M strain from Korea. The origin of these polymorphic P elements is discussed in relation to the hypothesis that they are descendants produced by mutational degradation from similar primordial P elements with P factor activity, which were created recently to a similar number per genome.

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A procedure to locate autosomal male-determining factors (A^M) of the housefly is described, which employs a female-determining factor (F) marked with a closely linked dominant gene. A total of 70 A^M chromosomes extracted from four II^M strains, nine III^M strains and three V^M strains of different geographic origins were examined. On the basis of female recombination frequencies, two to three types of A^M chromosomes were found in each of the linkage groups, suggesting that the A^M chromosomes are polymorphic for chromosome aberrations. All the A^M factors were mapped to a specific site or closely linked sites on the respective autosomes. From the comparison of the mitotic autosome figures and the female recombination maps of A^M chromosomes, it is suggested that A^M factors are located near the centromeres of autosomes. The validity of this technique and the possible mechanisms for the origin of M polymorphism are discussed.

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In order to consider characteristic chromosomal evolution, agamatoploidy in genus Carex, nuclear DNA content of metaphase plates in root tip of 50 cytologically stable strains belonging to 26 species of Carex collected in Japan was measured Feulgen cytophotometrically. Considerably large variation was observed in six species with rather high chromosome number. There was 7.7 times variation in DNA content among species analyzed in the present study. As assumed by earlier reports, it is presumed that C. siderosticta 4x and C. humilis were derived from C, siderosticta 2x and C. humilis ssp. nana, respectively. Among diploid species, 4.66 times but continuous variation was observed. There were no significant differences in nuclear DNA among four aneuploid of C. oxyandra and five of C. conica, respectively. Neither of five couples of strains, each belonging to a single species and having the same chromosome number but collected at different sites revealed any differences, indicating intraspecific aneuploid resulted from simple change of chromosome number. Three pairs of close relatives, C. foliosissima vs. C. morrowii, C. paxii vs. C. nubigera and C. pumila vs. C. kobomugi, were similar to each other in DNA content. It is clear that the increase in chromosome number is accompanied by the decrease in nuclear DNA content; negative correlation and regression between DNA content and chromosome number were confirmed to be highly significant in 45 diploid species. Based on the evidence of various kinds of earlier investigrtions and the present study, it is suggested that species with many small chromosomes would be derived from species having small number of large chromosomes by means of fragmentation followed by slight reduction of DNA.

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Karyotypes of T. apetalon (4x=20, SSUU) were analysed by the patterns of H-segments, which were revealed by cold treatment of the chromosomes. The types revealed in a given chromosome were numbered, e.g., A1, A2, A3 in chromosome A, etc. The karyotypes of individual plants were described according to a system exemplified by 3 plants from the Fujinosawa population (Fj), where the slash mark separates homoeologous pairs and the decimal mark homologous chromosomes:<br> Karyotype A B C D E Freq.<br> 6 1•1/3•3 7•7/6•6 5•5/2•2 2•2/5•5 5•5/4•4 1<br> 12 1•1/3•3 7•7/6•6 6•6/4•4 2•2/5•5 10•10/4•4 3<br> 38 1•1/3•3 7•7/6•6 5•6/2•4 2•2/5•5 5•10/4•4 1.<br> In Fj21 different homokaryotypes (32 plants), and 17 different heterokaryotypes (18 plants) with 1-3 heteropairs were identified among 50 plants examined, as in part presented in the above tabulation. Karyotypec structure of the other 3 populations was quite similar to the case of Fj. And the frequency of homozygosis of 10 pairs of homologous chromosomes was high in four different populations, ranging in percentage from 95.7 (Fj) to 99.6 (Mi- nakamidani, Mn). These high percentages indicate that reproductions is overwhelmed by selfing. Occasional outcrossing results in heterokaryotype, e.g., hybridization between karyotype 6 and 12 in Fj produces karyotype 38. Selfing of this heterokaryotype results in 6 recombinant and 2 parental homokaryotypes. Of the 6 recombinant types 3 homokaryotypes were actually observed, i.e., 7 1•1/3•3 7•7/6•6 5•5/4•4 2•2/5•5 5•5/4•4 4<br> 9 1•1/3•3 7•7/6•6 6•6/2•2 2•2/5•5 5•5/4•4 1<br> 16 1•1/3•3 7•7/6•6 6•6/5•5 2•2/5•5 5•5/4•4 2<br> The process mentioned above, i.e., occasional outcrossing followed by selfing, is the mechanism that explains how the population has become an assemblage of various homokaryotypes. With respect to all the chromosomes, A-E, four members successfully partitioned into a pair of homoeologous chromosomes, homologous chromosomes Present address : 1) Chikushino-danchi 16, Futsukaichi, Chikushinoshi 818. 2) Department of General Education, Kumamoto University, Kumamoto 860. 3) Biological Laboratory, Kumamoto being homozygous in 95-99 percent of the pairs. This is a reasonable result of the existence of various chromosome types or chromosomal variations in the diploid progenitors SS and UU, both of which are now extinct.

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HindIII digestion of chloroplast DNA (ctDNA) from normal (N) and male sterile (S) lines of sugar beet generated 26 (N ctDNA) and 25 (S ctDNA) discrete bands ranging in size from 0.45×10⁶ to 14.5×10⁶ daltons (d). Densitometric tracings and a Southern hybridization experiment revealed one band (H7) missing and replacement of this band by two fragments (H12b and H14b) in S ctDNA. A slight intraspecific heterogeneity is likely to be due to the creation of a new HindIII site in the left part of the large single-copy region of S ctDNA. The summation of HindIII fragments indicated a molecular weight of 97.38 (N ctDNA) or 97.53 (S ctDNA) ×10⁶ d. Southern hybridization analyses demonstrated that the chloroplast ribosomal RNA genes are located on three HindIII fragments of H4, H20 and H22, the large subunit (LS) gene of ribulose-1, 5-bisphosphate carboxylase/oxygenase on H6 and H17 fragments, the ribosomal protein CS-19 gene on 112 and H5a fragments and the 32, 000 d thylakoid protein gene on a H5b fragment. Twelve (derived from N ctDNA) and 18 (derived from S ctDNA) HindIII fragments have been cloned into pBR 322.

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Among 85 dominant meiotic mutants isolated after UV mutagenesis by the application of allelic complementation between inl (37401) and inl (38201(t)) on LG V, those mutants localized proximal to al-3 expanding putatively from ilv-2 to am on LG V were described. Twelve mutants Asc(KH2B88), Asc(KH2B95), Asc(KH2B124), Asc(KH2B129), Asc(KH2B132), Asc(KH2B241) , Asc(KH2B249), Asc(KH2B341), Asc(KH2B394), Asc(KH2B424), Asc(KH2B540) and Asc(KH2B755) were mapped to the relatively small area. Of these five mutants were found to produce abortive ascospores only when they were protoperithecial parent (class I) and two mutants expressed their traits independent of protoperithecial or conidial parent (class II). Five mutants were marginally sensitive to UV compared with that of a Mei-2 mutant used as a reference. At least three mutants showed relatively high aneuploid formation in LG V (15-19%) in the heterozygous zygotes. Two mutants showed low recombination recovery rates (23-36%) and four mutants locating distal side of this gene cluster showed elevated recombination frequencies between al-3 and inl, which were 2.5-3.5 times higher than that observed in wild type. From these observations at least 9 mutations were assumed to be derived from different genes and revealed the existence of meiotic gene cluster, designated V-1 at the area.

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Out of 85 dominant meiotic mutants, 10 mutations on LG V localized distal to his-1 were partially characterized. Of these, Asc(KH 2B 97), Asc (KH 2 B 380), Asc (KH 2 B 658) and Asc(KH 2 B 761) were closely linked to al-3. Asc(KH 2 B 380) and Asc(KH2 B 761) showed reduced recombination recovery rates and Asc(KH2 B 761) elevated recombination frequency between al-3 and inl 10-times higher than that observed in wild type. Though Asc(KH 2 B 97) and Asc(KH 2 B 761) produced aborted ascospores only when they were protoperithecial parents (class I), Asc(KH 2 B 380) and Asc(KH 2 B 761) were class II which produced aborted ascospores independent of protoperithecial or conidial parent. Asc(KH2 B 658) was marginally sensitive to UV compared with that of a Mei-2 strain (FGSC#2621). From these results, these four strains and Asc(KH2 A 83) (Furukawa and Hasunuma 1984) were assumed to be derived from different genes and constituted meiotic gene cluster, designated V-2. Asc(KH 2 B 36), Asc(KH 2 B 146) and Asc (KH 2 B 551) were mapped within relatively small area, putatively from met-3 to ad-7. Asc (KH 2 B 146) showed elevated recombination frequency between al-3 and inl, Asc(KH 2 B 36) showed class I and Asc(KH2 B 551) showed class II phenotype. Asc(KH 2 B 229), Asc(KH 2 B 300) and Asc(KH 2 B 630) were mapped at a more distal part of inl. Asc(KH 2 B 229) showed class II and Asc(KH 2 B 300) showed class III phenotype. Homozygous zygote of Asc(KH 2 B 300) showed reduced ascospore abortion and it was suggested to be a spore killer. Asc(KH 2 B 229) and Asc(KH 2 B 630) showed marginal sensitivity to UV compared with that of a Mei-2 strain.

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During the course of investigation of polyploid strains in rape (Brassica napus L.), a hypodiploid (2n=32) was found, that was assumed to be of parthenogenetic origin. This plant showed good fertility and produced seeds by open pollination. Chromosome number of its progeny ranged between 2n =33 and 38, i. e., between the chromosome numbers of their parent and the eudiploid (2n=38). Pollen and seed fertilities of the progeny showed significant correlations with their chromosome numbers. Plants increased their fertilities proportionally with the increased chromosome numbers. The chromosome configurations of these plants indicated that viable zygotes had to have at least 18 chromosomes out of 19 basic (haploid) chromosomes. This is the reason why all the plants obtained had more chromosomes than their parent. The tendency for the progeny to approach the diploid in their chromosome number was discussed in relation to the maintenance of euploidy.

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