Offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent.

Heterodisomy (heterogenous) indicates a meiosis I error.Isodisomy (homozygous) indicates a meiosis II error or postzygotic chromosomal duplication of one of a pair of chromosomes, and loss of the other of the original pair.

Uniparental is euploid (correct number of chromosomes). Most occurences of uniparental disomy (UPD) → normal phenotype.

Consider UPD in an individual manifesting a recessive disorder when only one parent is a carrier.

Examples: Prader-Willi and Angelman syndromes.