Punnett square 6

This is incorrect! 

Dr. Foster: ‘Let’s take a closer look at the scenario you just proposed. If the unaffected parent truly has no copy of the disease allele, their genotype must be AA. Having Aa would make them a carrier, which contradicts the idea that they are completely unaffected. That’s why Punnett square 6 doesn’t accurately represent the situation, since it assumes the unaffected parent is carrying a recessive allele.’