The mosaic chromosomal aneuploidy mutant (moa-1) of Arabidopsis thaliana was attained in a screen of Landsberg erecta (Ler) mutagenized seeds that had been chemically altered by ethylene methane sulfonate (EMS). Sieves of different mesh sizes were used to separate large seeds from normal seeds. The mutant line was recognized from one of these large seeds. Moa-1 has various phenotypic differences to wild type, including increasing flower and pod size, delayed petal abscission, reduced seed set, and increased seed mass. According to karyotype analysis, each moa-1 mutant plant's cells contain a different number of chromosomes, often between 11 and 18. In contrast, the cells of wild type Arabidopsis plants data showed that all moa-1 plants have an abnormal number of chromosomes and thus they were termed as mosaic aneuploids. Reciprocal cross-pollination between moa-1 and wild type showed that moa-1 behaves as Mendelian dominant allele, and is therefore suitable for cloning by well-established positional mapping techniques. The data also proposed that transmission of the moa-1 allele is reduced, particularly through the female parent. According to the findings, the mutant plant is a mosaic aneuploid. Therefore, identifying the gene responsible for this mutation is potentially useful in understanding the mechanism of mosaic aneuploidy and its role in cell division.