Problems for tutorial 6
In tomatoes, red (R) color is dominant to yellow (r) color and cut leaf (C) is dominant to potato leaf
A pure strain of red color, potato leaf plant is crossed to a yellow color, cut leaf plant and the F1 was test
crossed to a yellow color, potato leaf plant which yielded the following progeny.
250 red color, cut leaf
247 yellow, potato leaf
256 red color, potato leaf
262 yellow color, cut leaf
a) What ratio would you expect from a dihybrid test cross if the genes were assorting independently?
b) What statistical test would you use to test this ratio?
c) Is it necessary to use this test for this data?
No, the ratio is close.
d) What is the relationship between these loci?
The genes do not show linkage.
e) Diagram the cross
(give genotypes for the parents, F1 and test cross progeny)
red, potato (R/R ; c/c)
yellow, cut (r/r ; C/C)
F1 test cross
(R/r ; C/c)
yellow, potato (r/r ; c/c)
Test cross progeny
1 red, cut (R/r ; C/c)
1 red, potato (R/r ; c/c)
1 yellow, cut (r/r ; C/c) 1 yellow,
potato (r/r ; c/c)
In tomatoes, tall (D) vine and spherical (O) fruit are dominant alleles of dwarf (d) vine and oblate (o)
Two homozygous plants
were crossed and the F1 was test crossed to a dwarf, oblate plant which
yielded the following progeny.
406 tall, oblate
394 dwarf, spherical
93 tall, spherical
107 dwarf oblate
a) Why isn't it necessary to use the Chi - Square test to see if these two genes are assorting independently?
It is clear that this is not a 1:1:1:1 ratio.
b) What is the relationship between these two genes?
The genes are linked (or on the same
c) Diagram the cross (give genotypes for the parents, F1 and testcross progeny).
(there are two possibilities for the parents.
You should be able to tell which it is by looking at the test
F1 test cross
tall spherical ???? x dwarf oblate (d o/d o)
test cross progeny
Parental types — >>
tall oblate (D o/d o),
dwarf spherical (d O/d o),
Recombinant types----->tall spherical (D O/d o), dwarf oblate (d o/d o)
Even though you weren't told the exact genotype of the original parents (except that they were
homozygous) and F1's you should note that is possible to determine it from the F2. Write them out with
their correct phenotypes.