Suppose that seed size in a particular plant species is a polygenic trait. A grower crosses two different pure-breeding varietie
s of the plant, and measures seed size in the F1 progeny. She then backcrosses the F1 plants to one of the parental varieties and measures seed size in the backcross progeny. The grower finds that seed size in the backcross progeny has a higher variance than seed size in the F1 progeny. What is the most likely explanation for the higher seed size variability in the backcross progeny?
The size of a seed in a specific plant is transmitted as a polygenic trait. When crossing between two true-breeding varieties takes place, the heterozygous individuals are obtained in the F1 generation. When these F1 offspring are backcrossed with one of the parents, there will be an increase in the variance. This is due to the fact that the backcross progeny are not uniformly heterozygous at the seed size loci.
