Question

"These are the results of a three point cross in Drosophila for the three loci DEF: deF =89, dEf =36, DEF =299, dEF =587, def =321, DeF =42, DEf =98, Def =548. The map distance between the E and F loci is 13.12cM. The map distance between the D and F loci is 34.55cM. Calculate the Interference correct to 2 decimal places."

Answer 1

In the question we have been given the map distance between E and F = 13.12cM and distance between D and F = 34.55cM.

We have to find interference, given by 1 - Coefficient of coincidence ( C.o.c) so first we will find the C.o.c.

From this data and the progenies the order of genes is: dEF (587) compared with DeF ( 42) ------> F is same in both. Def (548) compared with dEf (36) ------> f is same in both. That means F/f lies in mid of D and E. So, order of gene is D-F-E.

And the given map distance or Recombination value (E-F) and (D-F) are independent of each other and the value of expected double cross over value between E and D can be predicted as product of the individual values of (E-F) and (D-F).

(E-F) = 13.12 cM or 13.12%

(D-F) = 34.55 cM or 34.55%

13.12% of 34.55%

= 13.12/100 * 34.55/100

= 0.0453 ---------------- expected double cross overs

Actual double crossover = DeF = 42 and dEf = 36

42 + 36 = 78

78/ total progenies= 1970

78/1970

= 0.03959

= 0.0396 ---------------- actual double cross overs

Coefficient of coincidence (C.o.c) =

actual double crossovers / expected double crossovers

C.o.c = 0.0396 / 0.0453

C.o.c = 0.8741

Or C.o.c = 0.87

Interference = 1 - C.o.c

= 1 - 0.87

= 0.13