Trisomic rescue

Trisomic rescue is a genetic phenomenon in which a fertilized ovum containing three copies of a chromosome loses one of these chromosomes to form a diploid chromosome complement. If both of the retained chromosomes come from the same parent, then uniparental disomy results. If the retained chromosomes come from different parents then there are no phenotypic or genotypic anomalies. The mechanism of trisomic rescue has been well confirmed in vivo, and alternative mechanisms that occur in trisomies are rare in comparison.
Many trisomic conditions result in stillborn infants. Trisomic rescue may be a natural means to keep a fetus as viable as possible. Indeed, spontaneous trisomic rescue has been observed in vitro. Similarly, monosomic rescue may also be a natural means to keep fetal viability via restoration of a disomic zygote.