Three monotelosomic alien addition lines (MtAALs: 2n=2x+1t) and one monoacrosomic alien addition line (MaAAL: 2n=2x+1a) of japonica rice cultivar Nipponbare, each carrying a single chromosome of a diploid strain of O. punctata (W1514) were isolated from the progenies of respective monosomic alien addition lines (MAAL: 2n=2x+1) for chromosomes 2, 4, 7 and 9 of O. punctata. Among them, three were classified as MtAALs carrying extra telocentric chromosomes 2 and 7, and an extra short arm of chromosome 9 in addition to the diploid complement based on the mitotic and meiotic chromosome analysis. The remaining one was similarly classified as a MaAAL carrying an extra acrocentric chromosome consisting of a complete short arm and a heterochromatic proximal region of the long arm of chromosome 4. Three MtAALs were designated as MtAALs 2, 7, and 9S (short arm of chromosome 9), respectively and one MaAAL was designated as MaAAL 4S(4L). Their morphology, seed fertility and the transmission rates of the extra chromosome were compared with those of the respective primary trisomics and MAALs. The plant morphology of MtAAL 2 and MaAAL 48(4L) was similar to that of the respective MAALs, while the plant morphology of MtAAL 9S was similar to that of the disomics. The plant morphology of MtAAL 7 was similar to that of the secondary trisomics for the short arm of chromosome 7. The seed fertility was higher than that of the respective MAALs, suggesting that the addition lines carrying a small chromosome fragment such as telosome or acrosome could give rise to functional gametes. The transmission rates of the extra chromosome were similar to those of the respective MAALs. Most of the PMCs in the MtAALs and the MaAAL showed a 12 II + 1 I (telosome or acrosome) configuration at the diakinesis and first metaphase. These facts suggest that the extra telocentric or acrocentric chromosomes originated from a misdivision of an alien univalent at anaphase I or anaphase II of the respective MAALs and the following chromosome breakage.
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