CSS 650 Advanced Plant Breeding
Midterm 2009
Name
___
Please show your work.
9 pts
1) In an open-pollinated landrace of corn, the purple stem characteristic is determined by a
single recessive gene. You grow a sample of this landrace in your garden and observe that 24
plants have purple stems and 126 plants have green stems. Assuming that the population is in
Hardy-Weinberg Equilibrium, how many of the green plants would you expect to be
heterozygous for this trait?
2) A breeder mixes equal quantities of seed of an A1A1B1B1 genotype and an A2A2B2B2
genotype to form a new, random-mating breeding population.
6 pts
a) What is the value of D (the disequilibrium coefficient) in the initial generation?
6 pts
b) What is the value of r2 in the initial generation?
6 pts
c) What value of D would be expected after one generation of random mating if the loci are
20 cM apart on the same chromosome?
1
9 pts
3) In an idealized population, the change in inbreeding in a single generation is F=1/2N.
Consider a breeding program for a cross-pollinating crop. List at least 3 factors that could
cause the effective population size Ne to be less than the apparent population size N in a
breeding population.
4) Assume that the parents in the mating scheme to the right are not inbred. A
8 pts
a) Which individuals in the pedigree are inbred? what are their
inbreeding coefficients?
B
C
D
E
4 pts
b) Use your results from part ‘a’ to determine the coancestry of A and D.
6 pts
c) What is the coancestry of C and D?
2
5) A random-mating population of pearl millet is segregating at the ‘A’ locus, which determines
grain protein content. The table below shows the frequency of genotypes and their genotypic
values.
6 pts
a) What are the coded values (a, d, -a) for these genotypes?
Frequency
Value
A1A1
0.49
14
A1A2
0.42
13.5
A2A2
0.09
12
Coded
Value
6 pts
b) Calculate the population mean on the original scale.
8 pts
c) If you crossed an A1A1 genotype with an A2A2 genotype, what would be the expected
breeding value of the progeny?
6 pts
d) What is the dominance variance for this locus?
3
8 pts
6) You harvest seed from a single plant in a large, out-crossing meadowfoam population. What
is the expected covariance among the progeny from that plant?
12 pts
7) You are discussing the concept of heritability with an animal geneticist. He maintains that
your definition is incorrect. How would you explain and defend the definition of heritability
that is commonly used by plant breeders?
4