Genetic 342 A&B Kenneth G Wilson Professory of Botany

Crosses Involving three or more pairs of genes

Trihybrid cross Independent Assortment

There are two possible solutions

• Classical Solution
• Simplify and Solve

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

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