You want to determine the linear order and genetic distance between three genes

Question

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 c; + o 245 9 + + 240 + m o 46gmo 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.

Explanation / Answer

The phenotypes of progeny

540     g m +

NCO

560       ++ 0

NCO

240 + mo

SCO

BETWEEN   m and 0

245      g++

SCO

162     +m+

SCO

170        g+0

SCO

BETWEEN   m and g

46         g m0

DCO

37      +++

DCO

Distance between m and o:

(240 + 245 + 46 + 37)/2,000 = 0.284*100 = 28.4 cM

============================================

Distance between m and g: (162 + 170 + 46 + 37)/2,000 = 0.2075*100 = 20.7cM

========================

g---------20.7cM --------------m--------28.4 cM ----------0

Expected DCO = 0.284*0.207 = 0.058

Observed DCO= (46 + 37)/2,000 = 0.0415

C= 0.0415/0.058 = 0.715

I= 1 – 0.715 = 0.285

Interference is positive, indicating that there were fewer double crossovers than expected

540     g m +

NCO

560       ++ 0

NCO

240 + mo

SCO

BETWEEN   m and 0

245      g++

SCO

162     +m+

SCO

170        g+0

SCO

BETWEEN   m and g

46         g m0

DCO

37      +++

DCO

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