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Cell Signalling and DNA Repair

emperature and Light

An illustration shows two rabbits side-by-side. The rabbit at left was reared at 20 degrees Celsius. It has a white body with black ears, nose, feet, and tail. The rabbit at right was reared at temperatures above 30 degrees Celsius. It is white with no black coloration on its body or extremities. Both rabbits have red eyes.

Figure 1: A pigment gene is influenced by temperature.Gene C controls fur pigmentation in Himalayan rabbits. Because the gene is active when environmental temperatures are between 15 and 25°C, the rabbit reared at 20°C (left) has pigmentation on its ears, nose, and feet, where its body loses the most heat. The rabbit reared at temperatures above 30°C (right) has no fur pigmentation, because gene C is inactive at these higher temperatures.© 2013 Nature Education Adapted from Pierce, Benjamin. Genetics: A Conceptual Approach, 2nd ed. All rights reserved. 

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In addition to drugs and chemicals, temperature and light are external environmental factors that may influence gene expression in certain organisms. For example, Himalayan rabbits carry the C gene, which is required for the development of pigments in the fur, skin, and eyes, and whose expression is regulated by temperature (Sturtevant, 1913). Specifically, the C gene is inactive above 35°C, and it is maximally active from 15°C to 25°C. This temperature regulation of gene expression produces rabbits with a distinctive coat coloring. In the warm, central parts of the rabbit’s body, the gene is inactive, and no pigments are produced, causing the fur color to be white (Figure 1). Meanwhile, in the rabbit’s extremities (i.e., the ears, tip of the nose, and feet), where the temperature is much lower than 35°C, the C gene actively produces pigment, making these parts of the animal black.

Light can also influence gene expression, as in the case of butterfly wing development and growth. For example, in 1917, biologist Thomas Hunt Morgan conducted studies in which he placed Vanessa urtica and Vanessa iocaterpillars under red, green, or blue light, while other caterpillars were kept in the dark. When the caterpillars developed into butterflies, their wings showed dramatic differences. Exposure to red light resulted in intensely colored wings, while exposure to green light resulted in dusky wings. Blue light and darkness led to paler colored wings. In addition, the V. urtica butterflies reared under blue light and V. io butterflies reared in the dark were larger than the other butterflies.