Chapter 10 - Differentiation and gene expression

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Ripening of fruit such as tomato involves a tightly regulated sequence of physiological transitions and changes in expression of several genes, with the plant hormone ethylene playing a coordinating role. The visible colour change from green to red is due to chlorophyll degradation and synthesis of red lycopene pigment. Around this time respiration rate increases, ethylene synthesis accelerates, cell wall softening genes are expressed aroma and flavour compounds are synthesised, and acids and starch are converted to sugars. Overall this packaging is an attractive food to many animals and the benefit to the plant is increased probability of seed dispersal.

(Photograph courtesy J.D. Hamill)

Simply, the organism is a unique result of both its genes and the temporal sequence of environments through which it has passed, and there is no way of knowing in advance, from the DNA sequence, what the organism will look like, except in general terms.

(R.C. Lewontin (1997) 'Genes, environment, and organisms', Hidden Histories of Science, ed. R.B. Silvers, 115-140, Granta Books: London)