Phenotypic Plasticity (College Board AP® Biology)

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

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