How do I find the genotype of each parent based on this question?

Question

A black, smooth guinea pig was mated with an albino, rough guinea pig. Their offspring were black rough and black smooth. These were the only types produced over a period of years in a number of matings. Black and rough are dominant traits. What was the probable genotype of each parent?

Answer 1

Let Black=B
Let Albino=b

Let rough=R
Let smooth=r

Now, we know that a black, smooth guinea pig crossed with an albino rough guinea pig produced black rough and black smooth guinea pigs.

We already know that the black pig has a genotype of rr for smooth and that the albino has a genotype of bb.

Since there were no albino offspring, we know that the black pig didn't have a recessive albino gene, giving it a genotype of BB. Now, the black pig has a total genotype of BBrr.

Since there were smooth offspring, this means that the albino guinea pig must have had the recessive smooth gene. So, its genotype is Rr. The total genotype for the albino pig is bbRr.

I hope that this helps.

Answer 2

Parents - black, smooth x albino, rough

F1 offspring - black, rough and black, smooth

Here's the logic you need to use:
-- All the offspring are black, so ALL offspring had to get the gene for black (B). This means that the black parent was BB.
-- The albino parent had to be bb because albino is recessive.

-- Some of the offspring have smooth coats, so each parent must have at least one r in order to give the offspring rr.
-- The smooth-coated parent had to have rr.
-- The rough-coated parent had to have an R to be rough and an r to have smooth-coated offspring.

So the parents are:
black, smooth BBrr
albino, rough bbRr