Uniparental disomy can be produced by several mechanisms involving nondisjunction in meiosis, nondis

Uniparental disomy can be produced by several mechanisms involving nondisjunction in meiosis, nondisjunction in the zygote, or early embryo. (a) Normally, gametes contain one copy of each chromosome, and fertilization produces a zygote carrying two copies of a chromosome—one derived from each parent. (b) Nondisjunction in both parents, in which one gamete carries both copies of a chromosome and the other gamete is missing a copy of that chromosome. Fertilization produces a diploid zygote, but both copies of one chromosome are inherited from a single parent. (c) Nondisjunction in one parent, resulting in the loss of a chromosome. This gamete fuses with a normal gamete to produce a zygote monosomic for a chromosome. An error in the first mitotic division results in duplication of the monosomic chromosome, producing uniparental disomy.