Please help answer.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC43917/pdf/pnas01133-0397.pdf

use this site article to answer the following question..

One possible method to localize chromosomal regions that
contribute to a phenotype when they are trosomic would be to
identify regions that are trisomic in all individuals with a
partial trisomy that exhibit the phenotype in question. In your own
words, explain why variable penetrance and expressivity of a
phenotype would make this approach less valid.