Phenotypic Plasticity
- Phenotypic plasticity is the idea that although genotype remains fixed throughout an organism's lifetime, the way that the phenotype is expressed can vary during this time
- An organism’s internal or external environment can influence gene expression patterns, and therefore phenotype
- The levels of regulatory proteins or transcription factors can be affected in response to environmental stimuli such as light, and chemicals including drugs and hormones
- For example, enzymes are activated in response to ultraviolet radiation and increase the expression and production of melanin, leading to skin pigmentation
- Temperature can also influence gene expression as demonstrated by organisms
- The Himalayan rabbit (Oryctolagus cuniculus L.) possesses a gene for the development of pigmentation in its fur
- The gene is inactive above 35°C but active between 15°C and 25°C
- In the parts of the body that are cooler such as ears, feet and nose the gene becomes active making these areas black
- The Himalayan rabbit (Oryctolagus cuniculus L.) possesses a gene for the development of pigmentation in its fur
Examples of Multiple Phenotypes for One Genotype
Flower color
- Can vary according to soil pH
- Flowers from the Hydrangea genus vary from blue blooms (acidic soil) to pink (alkaline soil)
- pH of the soil affects uptake of aluminum ions, which has a marked effect on the flower color
- More acidic soil contains a higher concentration of aluminum ions, which causes a blue coloration
CC BY-SA 4.0 Gretafrost, via Wikimedia Commons
Seasonal Fur Color in Arctic Animals
- Animals such as the snowshoe hare (Lepus americanus) change their fur color in winter and summer
- In winter, their fur is white, against the background of snow and ice
- In summer, their fur becomes brown, against a background of plants, soil and mud
- The color change is thought to be partly linked to daylength and the amount of light received during the day
- On shorter days, receptors in the retina transmit daylength information to the hare’s brain, stimulating the growth of white hair as opposed to brown, starting with the extremities
- White hair lacks the colored pigment melanin, and the space not taken up by melanin is though to create air pockets within the hairs for extra insulation
- This phenomenon is not believed to be coded for in the hare's genome
Snowshoe Hare Winter Coat Color
CC BY-SA 3.0 D. Gordon E. Robertson, via Wikimedia Commons
Sex Determination in Reptiles
- In certain reptile species, the temperature at which their eggs are incubated before hatching determines whether they are born male or female
- For example, the common snapping turtle (Chelydra serpentina) incubates its eggs in sand
- The eggs are born female at either cool (22°C or lower) or hot (28°C or above) temperatures
- Between these temperatures, males are born predominantly
The common snapping turtle
CC BY-SA 3.0 Leejcooper, via Wikimedia Commons
Other Examples of Phenotypic Plasticity
- In animals, the skin can darken after exposure to prolonged intense ultraviolet radiation eg. tanning from sun exposure
- A single tree can have leaves of varying size, shape color according to exposure to sunlight, wind and availability of nutrients
- Exercise alters a person's build and outward appearance
- Practising a task allows animals to become more skilled at that task eg. playing guitar