Male and female heterogameties are two distinct modes for genetic sex determination. In almost all mammals including humans, male is the heterogametic sex, while female is the heterogametic sex in all birds. The above fact has contributed to creating a long-standing idea among the researchers that “Heterogametic sex once fixed is not changed so easily to the other”. A marginally evolved recent idea, however, proposes that heterogametic sex could be changed to each other far more frequently than we ever expected. In fact, we can well see many cases of transitions in lower vertebrates. Among them, Japanese frog Rana rugosa is surprisingly unique, because it has already experienced the change of heterogametic sex from male to female three times, within its own lineage. The fourth change, moreover, seems to be on the verge of appearance at the central Japan stage. Why does heterogametic sex change so frequently in the frog? We review the sex determining systems and conduct a discussion on driving-force to change the heterogametic sex, particularly from a point of view of uniqueness of this situation in phylogeny of the frog and topography of Japanese Islands involved in the population dynamics.

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Chromosomal behaviour following mutagenic treatments was studied in M1 generation of chickpea, var. Pusa-212 and Pusa-372. A wide spectrum of meiotic aberrations was induced in the treated populations, the most frequent being stickiness of chromosomes, univalents, multivalents, laggards, bridges, cytomixis and disturbed polarity. Other anomalies such as non-orientation of bivalents, precocious separation, non-disjunction and unequal segregation of chromosomes were also recorded but comparatively in less frequency. The frequency of meiotic aberrations and pollen sterility increased with the increase in dose/conc. of the mutagen. Combination treatments were found to be most effective than separate treatments of gamma rays and ethyl methanesulfonate (EMS) in inducing maximum frequency of meiotic aberrations. Among various stages of meiosis, frequency of metaphase anomalies was more followed by anaphase and telophase. The coefficient of interaction for various combination treatments was less than additive with respect to the overall frequency of meiotic aberrations and pollen sterility. In general, var. Pusa-372 was more sensitive to mutagenic treatments than var. Pusa-212. The present findings reveal the potential of gamma rays, EMS and their combinations in inducing mutations and enhancing genetic variability in chickpea for isolation of economically important mutations in the segregating generations.

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In this study, kudzu (Pueraria lobata Ohwi), a new biomass plant widely grown in Japan, was investigated by chromosome karyotyping. Four strains of Japanese kudzu were examined, and all were found to contain 22 chromosomes. The 5S and 45S rDNA genes, which contain fundamental repeat sequences used in karyotyping, were determined by fluorescence in situ hybridization (FISH). Our results found one 5S rDNA locus and three 45S rDNA loci on the chromosomes of all four strains, which suggest that Japanese kudzu is not greatly differentiated at the cytological level. A further 11 chromosomes were identified, and the rDNA loci were mapped by chromosome image analysis system IV (CHIAS IV), following which kudzu chromosome karyotyping was performed. This is the first report of cytogenetic analysis of P. lobata, a Japanese kudzu.

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Lolium multiflorum Lam. is a forage known as annual ryegrass and stands out for the nutritional quality and adaptation to grazing and excessive water. Since it is a winter grass of widest distribution in temperate regions worldwide and has a great variability between and within populations, cytogenetic studies are important to support breeding programs and for the knowledge of genetic diversity. In this way, the present study evaluated the meiotic behavior of 17 genotypes of ryegrass collected in the Southern and Southeastern Brazil. For analysis we used the conventional protocol for meiotic studies by squash technique and staining with 1% propionic carmine. In general, plants presented regular meiosis with formation of seven ring-shaped bivalents and terminalized chiasmata. Six accessions showed differences in the number of chromosomes associated with the nucleolus, which could be one, two or three, indicating the occurrence of different transcriptional activity. Four accessions presented irregularities such as the occurrence of nontarget oriented, the presence of bridges and micronuclei.

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