Solution Found!
In a certain species of rats, black dominates over brown.
Chapter 3, Problem 15STE(choose chapter or problem)
Problem 15STE
In a certain species of rats, black dominates over brown. Suppose that a black rat with two black parents has a brown sibling.
(a) What is the probability that this rat is a pure black rat (as opposed to being a hybrid with one black and one brown gene)?
(b) Suppose that when the black rat is mated with a brown rat, all 5 of their offspring are black. Now what is the probability that the rat is a pure black rat?
Questions & Answers
QUESTION:
Problem 15STE
In a certain species of rats, black dominates over brown. Suppose that a black rat with two black parents has a brown sibling.
(a) What is the probability that this rat is a pure black rat (as opposed to being a hybrid with one black and one brown gene)?
(b) Suppose that when the black rat is mated with a brown rat, all 5 of their offspring are black. Now what is the probability that the rat is a pure black rat?
ANSWER:
Step 1 of 3
Let us denote A be the dominant black and let a be the recessive brown. Since the sibling rat is brown and brown is recessive, the sibling rat must have a genotype aa. The only way for black parents to have a brown offspring is if both parents have the genotype Aa.