Somatic chromosomes of two species in the genus Euhadra were observed using the air-drying methods supplying abundance of mitotic cells. The diploid numbers of E. dixoni and E. subnimbosa are confirmed to have 56 in each case. E. subnimbosa bears 21 pairs of metacentric and 7 pairs of submetacentric elements, while E. dixoni has 19 pairs of metacentric and 9 pairs of submetacentric chromosomes. They not only show the same fundamental number NF=112, but also have a secondary constriction in the approximal chromosomal position and in the same sized metacentric pairs. Consequently, the minor karyotypical difference found in the two suggests a close similarity cytologically, though they bear morphological differences.
A male WM strain rat with 4/7 translocation was obtained in the offspring born after γ-irradiation. The male with translocation was mated to the normal females, and 14 offspring was obtained. They were segregated to the translocation heterozygotes (7) and the non-translocation rats (7) as just expected. Among the latter rats, one had the XYY sex chromosomes which were suggested to be developed by non-disjunction of the Y element in the meiosis of the translocation male parent.