A black guinea pig crossed with an albino guinea pig produces 12 black offspring. When the albino is crossed with a second black one, 7 blacks and 5 albinos are obtained. What is the best explanation for this genetic outcome? Write the genotypes of the parents and offspring in the first cross, along with the genotypes of the parents and offspring in the second cross including the fraction of guinea pigs that are black and albino in the second cross.