anticipation in genetics

[Newyawk]

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not sure where to put this thread.

am a little confused about anticipation. my research indicates that repeats expand in gametogenesis due to meiotic instability. my main question is - does an individual with a premutation consistently produce gametes with similar numbers of repeats? or is there variation (i.e. one gamete has 100 repeats, another 300).

thanks!

 

[libertyyne]

not sure where to put this thread.

am a little confused about anticipation. my research indicates that repeats expand in gametogenesis due to meiotic instability. my main question is - does an individual with a premutation consistently produce gametes with similar numbers of repeats? or is there variation (i.e. one gamete has 100 repeats, another 300).

thanks!

Variation is my understanding. But there are thresholds where it almost becomes unavoidable.

 

[Naruhodo]

Libertyyne is on the money. Gametes may differ but will fall within the distribution expected to result from the parent's repeat size. It varies gene by gene what ranges of repeats are normal, premutation, full mutation, etc. But generally once you're in the premutation range the next generation is at some risk of having an expansion into the range that they may be affected by the clinical disorder.

If you're curious there are actually tables based on clinical data of what the risk is of a given repeat size expanding to a full mutation per pregnancy. Here is an paper describing this type of data for Fragile X: Expansion of the fragile X CGG repeat in females with premutation or intermediate alleles. - PubMed - NCBI

 

[Newyawk]

Libertyyne is on the money. Gametes may differ but will fall within the distribution expected to result from the parent's repeat size. It varies gene by gene what ranges of repeats are normal, premutation, full mutation, etc. But generally once you're in the premutation range the next generation is at some risk having an expansion into the range that they may be affected by the clinical disorder.

If you're curious there are actually tables based on clinical data of what the risk is of a given repeat size expanding to a full mutation per pregnancy. Here is an paper describing this type of data for Fragile X: Expansion of the fragile X CGG repeat in females with premutation or intermediate alleles. - PubMed - NCBI

Exactly what i was looking for. Thank you!