Hi there :)
I just took a biology exam for med school, and I personally thought of this question as a little weird/unfair, since I don't think the answer is 100% clear here:
"Both children have the same disease.
For which mode of inheritance would this be a typical family tree?"
Possible answers:
A) x-chromosomal dominant
B) x-chromosomal recessive
C) autosomal dominant
D) autosomal recessive
E) mitochondrial
So, here is my thinking:
The obvious answer would be autosomal recessive, the mother of the affected children brought in the second recessive gene.
BUT.. There is no way to give a definitive answer with only two siblings affected and zero info on their mom. We have to assume that no matter what, the mother brought in an affected allele, otherwise none of this works.
With that logic, we have no fucking clue which part of the moms genome was affected. It could be literally anything. How are we supposed to know, because noone else in the family tree is affected?!
Am I not seeing something here?
(Ofc. they are probably saying youll need to focus on the individuals seen in the family tree, but since there is a need for someone on the outside to bring in a sick allele, that argument falls straight out the door. :( )