Plant Breeding Methods (CS, HS 541)

Exercise 3 – Quantitative Genetics Review

Give complete answers, but be brief and specific. Show your work.

20 points total

1. What is the mean and variance for a population (where only 1 locus is segregating) consisting of the F2 of the cross BB x bb where BB yields 24, Bb yields 18 and bb yields 9 fruits per plot?


2. How could you measure directly all components of the epistatic variance (s2I) of a population?


3. A population with a mean yield of 19 fruits per plant was intercrossed, and 5 S0 plants were sampled from it with yields of 28, 21, 29, 16 and 19 fruits per plant each, respectively. The half-sib families derived from the 5 S0 plants had yields of 25, 21, 24, 15, and 20 fruits per plant, respectively. What is the breeding value (A) of the highest yielding S0?


4. A quantitative genetic study was run for lodging resistance in a population of sweet corn that had been wind-intercrossed several times during development. Given the following analysis of variance, estimate s2A, s2D, and h2N. Does the population have a high enough heritability to warrant single-plant selection for the trait?

  • 2 df Sets (S)
  • 9 df Blocks / S
  • 297 df Males / S MS=205
  • 1200 df Females/M/S MS=45
  • 4491 df Error MS=5


5. If the population in question 4 had a mean of 7 before selection, what would it be after 2 cycles of selection where the best 5% of the FS families in the population were intercrossed to form the next generation (assuming the variances are not changed by selection)?

Given – k for selection percentage: 1%=2.64, 2%=2.42, 5%=2.06, 10%=1.76, 20%=1.40, 50%=0.80.