Sentences with phrase «additional genes present»
If a woman with a strong family history of breast and ovarian cancers tests negative for the BRCA1 / 2 genes, that does not mean her relatives are not at risk, says Daly — her siblings could still carry the gene, or there could be additional genes present that predispose them to cancer that clinicians don't yet know how to test for.
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The disorder arises when some or all of an extra copy of chromosome 21 is present, but exactly how this additional set of genes disrupts development, leading to learning difficulties and other symptoms of Down's, isn't clear.
Trisomy 21 means that there are three copies of chromosome 21, and while not included in the CNV classification, it demonstrates the effects that can occur when additional gene copies are present on a massive scale.