Final answer:
To create a linkage map and determine gene order, we analyze recombination frequencies, with lower percentages indicating closer proximity on the chromosome. Given data suggests A and D are closest (13%), while B and C are not directly given but are assumed to be linked and less than 50%.
Step-by-step explanation:
To construct a linkage map and determine the order of genes on a chromosome based on given recombination rates, we first recognize that a lower recombination frequency suggests that genes are closer together.
The given recombination frequencies are A to B = 72%, A to D = 13%, and C to D = 25%. Since A to D is the lowest frequency, A and D are closest on the chromosome.
We do not have the direct recombination rate for B to C, but we can infer it to be high (higher than A to B) since A to B is already 72% and there's a 25% chance for C to D recombination.
To find the rate of recombination for B to C (B to C), we would typically add the recombination frequencies of B to A and A to C or subtract the recombination frequencies of A to C from A to B.
However, we have neither A to C nor B to C. Still, we can infer that B to C must be less than 50%, because if it were 50% or more, B and C would assort independently, and the genes would not be considered linked.
Knowing the arrangement of genes is A-D and that A-B and C-D have relatively high recombination percentages, we can assume that B and C face away from A. Therefore, the order of the genes could be represented as A - D - C - B.
We must be cautious as Sturtevant’s method is less accurate when genetic distances approach 50% because it becomes unclear whether genes are far apart on the same chromosome or on different chromosomes.
For detailed mapping, additional crosses examining the recombination between these genes and including more data points would be necessary.