Answer:
20 ( B )
Explanation:
Given data:
a and b are 10 map units apart
b and c are 20 map units apart
a and c = 30 map units apart
<em>condition </em>; Triple heterozygote testcrossed
number of progeny = 1000
<u>Determine the number of double crossover result </u>
P( crossover between a and b ) = 10/100 = 0.1
P( crossover between b and c ) = 20/100 = 0.2
p( double crossover ) = 0.1 * 0.2 = 0.02
hence number of double crossovers = number of progeny * 0.02
= 1000 * 0.02 = 20
