Final answer:
Among the options listed, Southern blotting is the most effective and cost-efficient method to test for the genetic variation associated with Fragile X syndrome. It is well-suited to detect mutations that cause this condition.
Step-by-step explanation:
Fragile X syndrome is diagnosed through genetic testing, which involves analyzing a person's DNA to detect the presence of specific genetic changes associated with the condition. Among the options provided, Southern blotting would be the most effective test for the variation found in Fragile X. Although whole-genome sequencing can provide comprehensive information, it is typically more expensive and not necessary for conditions like Fragile X, where the causative mutation is well understood. Southern blotting is specifically tailored to detect DNA variations like those seen in Fragile X and is thus a more tailored and cost-effective approach.