Trisomic rescue (also known as

trisomy A trisomy is a type of polysomy in which there are three instances of a particular chromosome, instead of the normal two. A trisomy is a type of aneuploidy (an abnormal number of chromosomes). Description and causes Most organisms that reprod ...

rescue or trisomy zygote rescue) is a genetic phenomenon in which a fertilized

ovum The egg cell or ovum (: ova) is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete is not capa ...

containing three copies of a

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

loses one of these chromosomes ( anaphase lag) to form a

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

chromosome complement. If both of the retained chromosomes come from the same parent, then

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. UPD can be the result of heterodisomy, in which a pair of non-identical chromosomes are inhe ...

results. If the retained chromosomes come from different parents (that is, one copy from each) then there are no phenotypic or genotypic anomalies. The mechanism of trisomic rescue has been well confirmed ''

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, an ...

'', and alternative mechanisms that occur in trisomies are rare in comparison. Many trisomic conditions result in stillborn infants (major exceptions include trisomies 13, 18, 21). Trisomic rescue may be a natural means to keep a fetus as viable as possible (though uniparental disomy may occur and result in syndromes such as Prader-Willi and Angelman syndromes due to genetic imprinting). Indeed, spontaneous trisomic rescue has been observed

in vitro ''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...

. Similarly, monosomic rescue may also be a natural means to keep fetal viability via restoration of a disomic zygote.

References

External links

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