PBG 650 Advanced Plant Breeding
First Midterm 2015
Name
Please show your work.
For multiple choice questions, circle the one best answer
6
6 pts
pts
1) You cross an AA genotype to an aa genotype. The F1 hybrid is backcrossed to the AA parent
to produce the first backcross generation (BC1). If the BC1 seed is planted and the
population is random-mated, what will be the expected genotype frequencies in the next
generation?
2) A breeder crosses an AAbb genotype to an aaBB genotype. The F1 hybrid is random-mated
to produce the F2. When the F2 generation is planted, 1/100 plants show the double
recessive phenotype (aabb).
5 pts
a) Assuming that the A and B loci have no effect on fitness, is there evidence for
disequilibrium in this population? Explain your answer.
b) Given that crosses were made by the breeder, what would be the most likely cause of
disequilibrium in this population? (you can answer this as a hypothetical question
regardless of your answer to question 2a)
5 pts
1
3) When there is no linkage, the expected rate of decay of disequilibrium with each generation
of random-mating is
5 pts
a) 25 %
b) 50 %
c) 100 %
d) It depends on gene frequencies
4) Circle one statement about random genetic drift that is NOT true.
5 pts
a) The variance in gene frequency among sub-populations increases over time
b) There is no change in the average gene frequency among sub-populations over time
c) The direction of the change in gene frequency in a sub-population can be predicted
d) There is a decrease in heterozygosity within sub-populations over time
5) Which of the following would NOT have a coancestry = 1.0?
5 pts
a) Plants from the same pureline variety of barley
b) Plants from the same clone of Douglas Fir (the state tree of Oregon)
c) Plants from the same inbred line of corn
d) All of the above (because none of them have a coancestry = 1.0)
7 pts
6) Explain the difference between stabilizing selection and directional selection. Use the
example of flowering time (e.g., days from planting until first bloom) in an outcrossing
species to illustrate why a breeder might want to use these types of selection to achieve
specific breeding goals.
2
7) An heirloom variety of carrots has been maintained by several members of a gardener’s
cooperative. Every year they each plant a small patch in their gardens, and allow it to crosspollinate, taking care that there is no other variety of carrots pollinating nearby. You plant
small quantities of seed from each gardener and score them for an SSR marker in the
laboratory. You tally the frequency of genotypes across all of the samples:
A 1A 1
60
6 pts
A 1A 2
60
A 2A 2
30
What is the inbreeding coefficient for this variety?
8) In an open-pollinated landrace of corn, the purple stem characteristic is determined by a
single recessive gene. The frequency of the recessive allele is 0.3.
6 pts
a) You grow a population of this landrace and remove all of the plants with purple stems.
What proportion of the plants that are remaining in your field will be heterozygous for
the purple trait?
b) If you allow the remaining plants to intermate, what is the new frequency of the allele
for purple stems that you would expect in this population?
6 pts
3
9) Assume that there is no prior inbreeding for any individuals shown in the pedigree below.
A
C
B
D
X
Z
a) Which individuals in the pathway are inbred?
5 pts
b) What is the coancestry of B and D?
6 pts
5 pts
c) The coancestry of B and D is equal to the inbreeding coefficient for _______.
d) What is the inbreeding coefficient for Z?
6 pts
4
10) A meadowfoam breeding population is grown in a field that is 10 miles from the nearest
commercial meadowfoam crop. Plants are spaced 3 feet apart and pollinated with
honeybees (i.e., they are randomly intermated). Seeds are harvested separately from each
plant and are evaluated in replicated progeny trials in the subsequent season. Offspring
from parent plant X are found to produce an average of 50 kg/ha more seed in comparison
to the mean for all progeny from the population.
a) What type of progeny were evaluated?
5 pts
i.
Half-sib families
ii.
Full-sib families
iii.
S1 families
iv.
We can’t tell
b) The breeding value of parent plant X is
5 pts
i.
0
ii.
25 kg/ha
iii.
50 kg/ha
iv.
100 kg/ha
11) A random-mating population of corn is segregating at the ‘A’ locus, which determines days
to flowering. The table below shows the frequency of genotypes and their observed
genotypic values:
Frequency Value
A 1A 1
0.36
60
A 1A 2
0.48
58
A 2A 2
0.16
50
a)
What are the coded genotypic values for each genotype (a, d, and –a)?
b)
What is the population mean on the original scale?
6 pts
6 pts
5