You want to determine the linear order and genetic distance

You want to determine the linear order and genetic distance between three genes on chromosome II in Drosophila. The recessive mutant alleles are g, m, and o. You cross heterozygous females to homozygous recessive males, score the phenotypes of progeny and obtain the following: 540 g m + 560 + + o 162 + m + 170 g + o 245 g + + 240 + m o 46 g m o 37+ + Determine the orientation of mutant vs. Wild type alleles on the female parent\'s chromosomes. Determine gene order (remember, what matters is which gene is in the middle). Calculate the distance between the three genes and draw the genetic map. Calculate interference and provide a brief verbal interpretation of your result.

Solution

Female parent genotype - g + m/ + o +

Here, g + m and + o + are parental class, so, non cross over = 540+560=1100

Frequency of D.C.O= {(46+37)/2000}*100= 4.15%

Frequency of first S.C.O = {(162+170)/2000}*100=16.60%

Frequency of other S.C.O = {(245+240)/2000}*100 = 24.25%

b) Comparing parental type with D.C.O type, we found that o is uncommon, so o is placed in the middle. So, gene order - g------o---------- m

c) So, map distance between g and o- (16.60+4.15) = 20.75cM and

map distance between o and m - (24.25+4.15) = 28.40 cM.

d) Expected D.C.O - {(20.75/100)*(28.40/100)} = 0.0589

Observed D.C.O - (4.15/100) = 0.0415

C.O.C = Observed D.C.O/Expected D.C.O = 0.0415/0.0589 = 0.704

Interference = 1-0.704 = 0.296

As the interference value is between 0 and 1 thus it indicates partial interference.