NBME 17
Could sb explain this please?
why not 2,2
It’s asking if the child is NOT affected… So if you start from the top and follow the affected pattern and unaffected, it goes like this:
Unaffected mom - 1,3 gives 3 to son (1 from dad is affected) -> this dad must pass his mom’s unaffected 3 to his child and the 2 comes from baby’s mom who is also unaffected resulting in 2,3. Baby can’t 2,2 because dad’s side doesn’t have a 2 and baby must get one from each parent.
This is autosomal dominant disease . Father is hereozygous affected (1,3) … mom is normal (2,2)… child is unaffected !!
The marker of affected gene is marker 1( from affected father of first generation (1,1) . If child is unaffected then he will never has marker1( of mutant gene ) , so child will have nsorsml gene from his father with has marker 3 , and normal gene from his mother marker 2, so child is (2,3)