Crosses Involving three or more pairs of genes

Trihybrid cross Independent Assortment

There are two possible solutions

Simplify and Solve

In Drosophila the following wild type alleles are used for analysis v (vermilion eyes), cv (cross-veinless) and ct (cut or snipped wing edges). Flies doubly recessive and homozygous (v+v+,cvcv,ctct) are crossed with flies singly recessive and homozygous (vv, cv+cv+, ct+ct+). Female progeny that are vv+, cvcv+, ctct+ are then test crossed with the tripley recessive males (vv, cvcv, ctct)

v

cv+

ct+

580

v+

cv

ct

592

v

cv

ct+

45

v+

cv+

ct

40

v

cv

ct

89

v+

cv+

ct+

94

v

cv+

ct

3

v+

cv

ct+

5

     

1448

cv+

ct+

580

cv

ct

592

cv

ct+

45

cv+

ct

40

cv

ct

89

cv+

ct+

94

cv+

ct

3

cv

ct+

5

   

144 8

Again we can rewrite the data as follows

cv+

ct+

580+9 4

cv

ct

592+8 9

cv

ct+

45+5

cv+

ct

40+3

   

1448

% recombination between cv and ct = (45+5+40+3)/1448 = 93/1448 = 6.4 % or 6.4 map units.  Thus the distance from the cv locus to the ct locus is 6.4 mu apart.
If we ignore the vermilion gene we can rewrite the data as follows:
Ignore cv Ignore ct

v

ct+

580

v+

ct

592

v

ct+

45

v+

ct

40

v

ct

89

v+

ct+

94

v

ct

3

v+

ct+

5

   

1448

 

v

cv+

580

v+

cv

592

v

cv

45

v+

cv+

40

v

cv

89

v+

cv+

94

v

cv+

3

v+

cv

5

   

1448

 
Rewrite   Rewrite  

v

ct+

580+45

v+

ct

592+40

v

ct

89+3

v+

ct+

94+5

   

1448

 

v

cv+

580+3

v+

cv

592+5

v

cv

45+89

v+

cv+

40+94

   

1448

 
The percent recombination between v and ct is calculated as follows: % recombination = (89+3+94+5)/1448 = 191/1448 = 13.2 % or 13.2 mu   The percent recombination between v and cv is calculated as follows: % recombination = (45+40+89+94)/1448 = 268/1448 =18.5 % or 18.5 mu  
The Recombination Frequencies for each pair of genes is: v---cv =18.5% cv--ct = 6.4 % ct--v = 13.2 %

Map data

v<---13--->ct<--6.4-->cv

 


Text iGenetics by Peter J. Russell


This web site is provided for instruction in Botany and Zoology 342

by Kenneth G. Wilson,
Professor of Botany
Miami University
wilsonkg@muohio.edu