Environmental Effects On Phenotype

Unit (5): Heredity

Chapter: Environmental effects on phenotype

Reference: Environmental factors, Siamese cats, Presence of drugs, Temperature

Learning objectives

  • To understand the effect of environment on phenotype of organisms by examples

Environmental factors

Environmental factors such as diet, temperature, oxygen levels, humidity, light cycles, and the presence of mutagens can all impact which of an animal's genes are expressed, which ultimately affects the animal's phenotype.

Genotype generally remains constant from one environment to another, although occasional spontaneous mutations may occur which cause it to change. However, when the same genotype is subjected to different environments, it can produce a wide range of phenotypes. There is a complex interaction between the genotype and the environmental factors of an organism that can lead to variable phenotypes.

Examples of some cases where environment affected the phenotype

Siamese cats

  • In Siamese cats, the coat color is highly sensitive to changes in temperature.
  • These cats show partial albinism due to a mutation in an enzyme involved in the production of melanin.
  • The enzyme is active in colder areas of the skin, which results in a darker colour, while it’s inactive in warmer regions of the skin resulting in a lighter colour.
  • This results in the breed’s characteristic dark fur on the face and on the extremities.

Presence of drugs

Due to the presence of drugs or chemicals in an organism's immediate environment can also influence gene expression in the organism.

  •  For example, C. R. Stockard showed that the Fundulus heteroclitus fish developed just a single eye when the fertilized egg was placed in the magnesium chloride solution.

Temperature

  • 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.
  • 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 colouring.
  • In the warm, central parts of the rabbit's body, the gene is inactive, and no pigments are produced, causing the fur colour to be white.
  • 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

  • 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 i.o caterpillars 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 coloured wings, while exposure to green light resulted in dusky wings.
  •  Blue light and darkness led to paler coloured 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.

  Summary

  • When the same genotype is subjected to different environments, it can produce a wide range of phenotypes.
  • In Siamese cats, the coat colour is highly sensitive to changes in temperature.
  • Due to the presence of drugs or chemicals in an organism's immediate environment can also influence gene expression in the organism
  • 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
  • Light can also influence gene expression, as in the case of butterfly wing development and growth.

 

 

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