Final answer:
The probability of a double crossover in the specified chromosomal region is 0.825% (none of the answers options provided). This value is calculated by multiplying the individual crossover probabilities for each of the two intervals.
Step-by-step explanation:
The probability of a double crossover in this chromosomal region, assuming no interference, is calculated by multiplying the probability of each crossover event. The distance between genes x and y is 7.5 map units, and the distance between y and z is 23.1 map units. Since 1 map unit (cM) corresponds to a 1% recombination frequency, we can use these distances to estimate the crossover probabilities.
Evaluating a double crossover: the chance of a crossover between x and y is 7.5%, and between y and z is 23.1%. Multiplying these gives (7.5/100) * (23.1/100) = .00825, or 0.825%, probability of a double crossover is c) 0.825% after converting to percentage. The options might have been based on incorrect calculations or assumptions, thus it's important to address this with your teacher.