Objective:To present the molecular cytogenetic characterization of de novo partial trisomy 7p (7p21.1→pter)and partial monosomy 9p(9p24.2→pter)associated with only mild mental retardation.Methods:Routine G-banding was performed to analyze the karyotypes of the patients and their parents,and array SNP was used for fine mapping of the aberrant region.Results:The patient presented with only mild mental retardation.The mother had normal karyotype,The father had an apparent translocation involving chromosomes 7 and 9 [46,XY,t(7;9)(p21.1;p24.2)],the karyotype of the child was ascertained as 46,XX,der(9)t(7;9)(p21.1;p24.2).Array SNP finely mapped the duplication to 7p21.1-7p22.3,a 19.6Mb region and the deletion to 9p24.2-24.3,a 3.80Mb region.Conclusion:These results suggested that partial trisomy 7p was primary cause for the phenotypic abnormalities and mental retardation of the patients,whereas a mild phenotypic effect was observed in the patient parental karyotype analysis could help define the aberrant type and recurrent risk evaluation.In contract to routine karyotype analysis,aberrant regions could be mapped by array SNP with higher resolution and accuracy.