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Uniparental disomy
Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or of part of a chromosome, from one parent and no copy from the other parent. UPD can be the result of heterodisomy, in which a pair of non-identical chromosomes are inherited from one parent (an earlier stage meiosis I error) or isodisomy, in which a single chromosome from one parent is duplicated (a later stage meiosis II error). Uniparental disomy may have clinical relevance for several reasons. For example, either isodisomy or heterodisomy can disrupt parent-specific genomic imprinting, resulting in imprinting disorders. Additionally, isodisomy leads to large blocks of homozygosity, which may lead to the uncovering of recessive genes, a similar phenomenon seen in children of consanguineous partners.
==Pathophysiology==
UPD can occur as a random event during the formation of egg or sperm cells or may happen in early fetal development. It can also occur during trisomic rescue.
* When the child receives two (different) ''homologous chromosomes'' (inherited from both grandparents) from one parent, this is called an heterodisomic UPD. Heterodisomy (heterozygous) indicates a meiosis I error.
* When the child receives two (identical) replica copies of a single ''homologue'' of a chromosome, this is called an isodisomic UPD. Isodisomy (homozygous) indicates either a meiosis II or postzygotic chromosomal duplication.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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