Based on the pedigree charts, what is going on in both of the pedigrees regarding the pattern of inheritance of the traits that are shown in the...

This question traces a genetic disorder in two different families using pedigree analysis.

In pedigree chart I, the parents are an unaffected male and an affected female. All of their children in the F1 generation are affected and have inherited the condition. In the F2 generation, only children of affected mothers from the F1 generation, inherit the condition. 

Mitochondrial DNA and its complement of genes is passed down from mother to offspring. The father's sperm does not contribute any of the mitochondrial genes to his offspring. Therefore, chart I shows the inheritance of mitochondrial DNA (including any genetic condition) from an affected mother to all of her offspring. 

In the second pedigree labeled J, the father is affected and the mother is not. All of their children in the F1 generation are unaffected and all of the offspring in the F2 generation are unaffected as well. To restate, fathers do not pass down their mitochondrial DNA to their offspring which is why the condition is only seen in the father in chart J.