Question

(3) The following is a list of loci from Drosophila melanogaster that have been mapped via linkage studies. The symbols for the loci have been shortened to one letter, and map distances have been rounded. Here are the map distances, in cM, for all pair-wise combinations of the 7 loci: c-d 50 d-s 50 f-y 3 c-f 11 d-t 12 s-t 50 c-s 7 d-w 50 s-w 19 c-t 50 d-y 50 s-y 21 c-w 12 f-s 18 t-w 50 c-y 14 f-t 50 t-y 50 d-f 50 f-w 1 w-y 2 How many linkage groups are defined by these loci? Draw a map for each linkage group with the locus positions indicated. Include the distances between each neighbor. Example: y                      x                      z             4                      8          Your map(s):

Answer 1

distance between two linked genes is the recombination frequency between genes.

If two genes are not linked to each other the recombination frequency between genes is 50%, so if the distance between two genes is 50 cM, then those genes are not linked.

here there are two linkage groups.

distance between d-c, d-s, d-w, d-w, d-y is 50 cM and distance between t-c, t-w, t-y, t-f,t-s is also 50 cM, so t and d belongs to another linkage group.

distance between d and t=12 cM

distance between s and w= distance between f and s+ distance between f and w

so order of genes is s, f, w.

distance between c and y=14 cM

distance between c and w= 12 cM

distance between w and y= 2 cM

distance between c and y= distance between c and w + distance between w and y

so order of genes is c, w, y.

distance between s and c= 7 cM

distance between c and f= 11 cM

distance between c and s= 18 cM

so

distance between c and s= distance between s and c +distance between c and f

distance between f and y = 3 cM

distance between f and w= 1 cM

distance between w and y = 2 cM

distance between f and y =distance between f and w+distance between w and y

map of linakge groups are