Question

P1: A female heterozygous for white (w), yellow (y) and miniature (m) – (all 3 recessive mutations) is crossed to a male who is mutant for all three traits.

The F1 male progeny phenotypes are:

+ + m

2278

w y +

2157

w y m

1203

+ + +

1092

+ y m

49

w + +

41

+ y +

2

w + m

1

Total =

6823

Was there positive or negative interference in the number of double crossovers, if so, to what extent?

		Negative, 0.9
		Positive, 0.1
		Zero interference
		Positive, 0.9
		Positive, 0.5

Answer 1

Interference = 1- Coefficient of coincidence

Coefficient of coincidence:

number of observed double cross overs / no. of expected double cross overs

number of observed double cross overs: 2+1=3

no. of expected double cross overs = expected double crossover frequecy*total progeny

expected double crossover frequecy= frequency of single crossover in the first region*frequency of single crossover in the second region*

Frequency of single cross over:

a) single cross over between m and + = 1203+1092+2+1/6823=0.45

b) single cross over between y and + = 49+41+3/6823=0.0136

expected double cross over frequency =0.45*0.0136=0.00612

no. of expected double cross overs =0.00612*6823=41.7

which makes the coefficient of coincidence = 3/41.7=0.071

Interfernce = 1-coefficient of coincidence = 0.929

Thus, interfernce is negative