Answer;
-Red eyes/ white eyes
Step-by-step explanation;
-Morgan discovered a single male fly with white eyes. He mated this mutant white-eyed male with a red-eyed (wild-type) female. The F1 generation all had red eyes (wild-type is dominant).
-The F2 generation showed the 3:1 red:white eye ratio, but only males (1/2) had white eyes. Morgan deduced that the white eye mutant allele must be located on the X chromosome.
-Alfred H. Sturtevant, Morgan's student assumed that if crossing over occurs randomly,the probability of crossing over between two genes is directly proportional to the distance between them.
-He used recombination frequencies to assign genes a linear position on a chromosome map and defined one map unit (centimorgan) as1% recombination frequency.