Multiply ¼ by itself for the first child and list the rest as unaffected

Ana: ‘If we just set ¼ for the first child being affected and multiply ¾ for the other three, that only covers one birth order. We’d ignore any permutations for which child is affected.’

Dr. Antoniou: ‘Exactly, that scenario might correspond to the first child alone being aa. But what if Child 2 was the one affected? Or Child 4? That method wouldn’t include those possibilities.’

Try again: