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Pedigree Analysis - Determining Type of Inheritance Pattern of a Trait

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sam777:
Given, the helpful responses, I think for this question, the answer would be B:
Because if the trait expressed an X-linked recessive inheritance, then an affected mother would pass on the trait to all sons (Because all sons get their X chromosome from the mother and their Y from the father). However, II6 is unaffected, and not possibly a carrier, given that the trait is being considered as X-linked.
Though correct me if I'm wrong  ;D

Billuminati:

--- Quote from: sam777 on September 30, 2021, 10:14:36 pm ---
Wow! That's a great way of determining the inheritance pattern. Could I also just confirm that a trait that has an autosomal recessive inheritance doesn't always skip generations, but has the ability to? So if you get no for: "Does it skip generations?" you can't be 100% certain that it is autosomal dominant? Would you then look at the prevalence in general? Such as whether most offspring with affected parents are also affected? But then this also can't prove it for certain, given that there is an element of chance involved, and that the phenotypic ratios of the offspring only indicate what is likely.

--- End quote ---

A more accurate way of phrasing "dominant traits don't skip generations" is that if they disappear from a lineage, they don't reappear. Autosomal recessive traits don't skip generations only if both parents are affected, it won't skip generations as all of their children will be affected too. Not many people with genetic diseases decide to have kids with each other. They often seek genetic counselling to determine their risk of transmitting the disease to their potential children, and the job of a genetic counsellor is to help them make an informed decision without judging them (a huge no-no would be telling them that "you can't reproduce because your kids will be affected", that's essentially Hitler and communist Chinese behaviour).

Billuminati:

--- Quote from: sam777 on September 30, 2021, 10:23:30 pm ---Given, the helpful responses, I think for this question, the answer would be B:
Because if the trait expressed an X-linked recessive inheritance, then an affected mother would pass on the trait to all sons (Because all sons get their X chromosome from the mother and their Y from the father). However, II6 is unaffected, and not possibly a carrier, given that the trait is being considered as X-linked.
Though correct me if I'm wrong  ;D

--- End quote ---

And yes, you are correct that you can only rule out X-linked recessive here, if it were the case, all sons of an affected mother will also be affected, but II-6 is unaffected

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