Chromosomal Rearrangment

Question

Recessive genes a, b, c, d, e, and f are closely linked on a chromosome, but their order in unknown. Three deletions in the regions are examined. One deletion phenotypically uncovers a, b, and c; another uncovers d, e, and f, and the third uncovers c and f. Please determine the order of these genes.

Answer 1

From the phenotypes of these three deletions we know that a, b, and c must be linked in one group, and that d, e, and f must be linked in another group. We also know that c and f must be next to each other. Neither a, b, d, nor e can be in between c and f because those phenotypes do not show up in the c and f deletion.

So c and f must be in the middle of this group of 6 genes. Genes a and must be on the side of c opposite of gene f, and d and e must be on the side of f opposite gene c. However, these data do not give enough information to determine the relative orders of a and b, and we also cannot determine the orders of d and e,

So there are four possibilities:

a - b - c - f- e -d

a - b - c -f - d - e

b - a - c - f - e - d

b - a - c - f - d - e

Hope this helps.