We can divide this question to two parts: Yy and TT. First, the parents have Yy(1) and Yy(2). The offspring may have four types: Y1Y2, Y1y2, Y2y1, y1y2. So the probability of getting Yy is 1/2. The same, the probability of getting TT is 1/4. So the final probability of YyTT is (1/2)*(1/4)=1/8