PLNT 4330 Tutorial 2
Altered Segregation
1) The shape of radishes may be long (LL), round (L’L’), or oval (LL’). Colour may be red
(RR), white (R’R’), or purple (RR’). If a long white strain is crossed with a round red
strain, what phenotypic proportions are expected in the F1 and F2?
2) What are the test cross generation’s genotypic and phenotypic ratios for the test crosses of
dihybrids (i.e., F1 crossed to aabb genotype), which display the following types of epistasis in the
F2?
a. Single recessive epistasis (i.e. AaBb x aabb)
b. Single dominant epistasis
c. Duplicative recessive epistasis
d. Duplicate dominant epistasis
e. Recessive and dominant epistasis
3) A corn geneticist worked with two different strains of corn, one abnormal for chromosome
10, the other normal for chromosome 10. The gene C (coloured kernels), c (colourless kernels)
was studied in a series of crosses.
Cross I:
F1:
C (abnormal chr 10), c (abnormal chr 10)
(coloured phenotype)
Selfed
F2:
18,295 coloured kernels
:
6,095 colourless kernels
Cross II:
F1:
C (normal 10), c (normal 10)
(coloured phenotype)
Selfed
F2:
12,040 coloured kernels
:
3,960 colourless kernels
Cross III:
F1:
Female heterozygote
C (abnormal 10), c (normal 10) x
male testcross
c (normal 10), c (normal 10)
TC1:
27,799 coloured kernels
17,724 colourless kernels
:
Cross IV:
F1:
Female heterozygote
c (abnormal 10), C (normal 10) x
TC1:
18,647 coloured kernels
male testcross
c (normal 10), c (normal 10)
:
26,833 colourless kernels
Fully explain these results. Statistical analyses are not required.
4) A wheat geneticist worked with two different strains of wheat, one resistant to stem rust
(Timstein), and one susceptible to stem rust (Chinese Spring). The gene Sr11 (stem rust
resistant) and sr11 (stem rust susceptible) was studied in a series of crosses as follows:
Cross I:
Female (F1 of Timstein x Chinese Spring cross)
F1:
Sr11 sr11
x
TC1:
17,875 stem rust resistant
:
Cross II (reciprocal cross of Cross I):
Female (testcross)
F1:
sr11 sr11
x
TC1:
:
14,830 stem rust resistant
Cross III:
Chinese Spring
P:
sr11 sr11
male (testcross)
sr11 sr11
17,857 stem rust susceptible
male (F1 of Timstein x Chinese Spring cross)
Sr11 sr11
0 stem rust susceptible
Timstein
Sr11 Sr11
F1:
Sr11 sr11
Selfed
(stem rust resistant)
F2:
13,325 stem rust resistant
:
0 stem rust susceptible
Fully explain these results. Statistical analyses are not required.