How to Analyze Autosomal Dominant Pedigree Trait?

In order to analyze this pedigree for autosomal dominant trait, we need to check whether the above pedigree is dominant or not.

For a dominant trait, it needs to follow two conditions:

a. No skipping of generation
b. Either of the parent should be affected to transfer the disease to their offspring

Note: If both parents are normal and their offspring are also normal then we do not consider skipping of generation.

Now, if you see the above pedigree, it fulfills both conditions. There is no skipping of generation, and disease has only passed to the next generation of either or both the parents are affected.

Note: The best way to analyze a pedigree is to check the X-linked trait first. So, if the above pedigree is an X-linked Dominant then it needs to follow DDD rule.

DDD rule states that if a trait is dominant and dad is affected, all his daughters will also be affected, but that is not the case here. So, the above pedigree shows autosomal dominance.