一般在染色体组成内的片段易位不导致表型异常,除非这种易位涉及遗传物质的增加或丢失。然而,Breg等(1972)发现,在明显平衡染色体重排的个体中,智力低下和多发性先天畸形的频率增高;而Funder-burk等(1977)报告,这种频率的增高,首先涉及非罗伯逊易位。作者选择了13例具有明显平衡染色体重排的病人,这些病人是通过对智力低下儿童的细胞遗传学研究,或通过对表型异常儿童的染色体分析查出来的。细胞遗传学研究是 Fragment translocations generally within the chromosomal makeup do not result in phenotypic abnormalities unless such translocations involve the addition or loss of genetic material. However, Breg et al. (1972) found an increased frequency of mental retardation and multiple congenital malformations in individuals with a clear balance of chromosomal rearrangements; Funder-Burk et al. (1977) reported an increase in this frequency, first involving non-Robertson Translocation. The authors selected 13 patients with well-balanced chromosomal rearrangements identified by cytogenetics in children with mental retardation or by chromosomal analysis of children with phenotypically abnormalities. Cytogenetics research is