We Saw That Southern Blotting of DNA from the βᴬ

Essay

We saw that Southern blotting of DNA from the βᴬ allele produces two DNA bands corresponding to fragment lengths of 1150 bp and 200 bp based on the location of two DdeI sites.In contrast,Southern blot analysis of βˢ-allele DNA produces a single DNA restriction fragment,measuring 1350 bp in length,since one of the DdeI sites is altered by SNP variation.Why is Southern blotting necessary to identify the correct bandsif you know the sizes,why can't you just identify your band on a gel? Why is the location of the probe (spanning the predicted lost DdeI site)important?