ABSTRACT

Aneuploidy is the term used to describe gross chromosomal imbalance in an organism or embryo, presenting as either additional (e.g., trisomy) or missing (e.g., monosomy) chromosomes. Aneuploidy arises during cell division when chromosomes fail to separate equally between the two new daughter cells [1]. Aneuploidy may be present in all the cells of the body and extra embryonic membranes, or it may be represented in a conceptus having both normal and aneuploid cells (so-called mosaicism). The consequences of aneuploidy constitute a wide phenotypic spectrum from early embryonic arrest to mild infertility, with the best-known being Down syndrome (trisomy 21) and rst trimester spontaneous abortion (mostly trisomies and monosomy X). The origins of aneuploidy lie in the meiotic divisions (principally in the ovary) and the early cleavage divisions of the preimplantation embryo. Arising by either nondisjunction, precocious separation of sister chromatids, or anaphase lag [1], the impact of aneuploidy on families can be devastating, for example, when faced with pregnancy loss, stillbirth, or a severely affected child. In all cases, aneuploidy results in an unfavorable outcome for the family in question and is undoubtedly a major contributing factor to the relatively low fecundity of humans compared with other species.