When I was an Honours student 50 years ago I was interested in the relationship between plant growth and energy capture by chlorophyll in a plant’s leaves. Using the model plant Arabidopsis I compared the growth and chlorophyll content of a wildtype line, a variegated mutant and their first generation hybrid (F1).
The advantage of using Arabidopsis was that it has a very short time from seed to plant and back to seed again. This meant that I could grow the parents, hybridise them and then grow the parents and their progeny to see how different levels of chlorophyll affected their growth – all within a term and a half at university.
The results showed that the level of chlorophyll per unit leaf weight was linearly related to the genotypes. Not surprisingly the variegated mutant parent had the lowest level of chlorophyll per unit leaf weight; the hybrid was intermediate; and the wildtype line had the highest level of chlorophyll. The increase was in a nice straight line, showing that the presence of the wildtype chlorophyll gene had what geneticists call an “additive” effect.
However, the effect on growth was completely different. The F1 hybrid was twice as big as its wildtype parent and three times greater than the variegated mutant parent. This is what geneticists call overdominance, and was surprising because one might expect that more chlorophyll...
