Environmental Factors & Phenotype (College Board AP® Biology) : Study Guide

Phenotypic plasticity

• Phenotypic plasticity occurs when individuals with the same genotype exhibit different phenotypes in different environments, due to differences in environmental conditions

• It is the idea that although genotype remains fixed throughout an organism's lifetime, the way that the phenotype is expressed can vary 

• 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

  • Temperature can also influence gene expression as demonstrated by organisms

Examples of phenotypic plasticity

Height and weight in humans

• Human height and weight are influenced by both genetics and environmental factors such as nutrition and lifestyle

  • Children who lack good nutrition can show limited growth, even if they possess genes for a tall stature

Flower color

• Flower color can vary according to soil pH

• Flowers from the Hydrangea genus vary from blue blooms (acidic soil) to pink (alkaline soil)

• This shows how environmental chemistry affects gene expression for pigments

CC BY-SA 4.0 Gretafrost, via Wikimedia Commons

Seasonal fur color in Arctic animals

• Animals such as the snowshoe hare or artic fox change their fur color in winter and summer

• The color change is thought to be partly linked to daylength and the amount of light received during the day

  • On shorter days (in winter), 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

  • In summer, longer daylight and warmer temperatures lead to brown or gray fur

• This phenomenon is not believed to be coded for in the hare's genome

CC BY-SA 3.0 D. Gordon E. Robertson, via Wikimedia Commons

Sex determination in reptiles

• In certain reptile species such as turtles, crocodiles, and some lizards, the temperature at which their eggs are incubated before hatching determines whether they are born male or female

• E.g. the common snapping turtle 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

Effect of increased UV on melanin production in animals

• Higher UV radiation exposure increases melanin production in human skin and other animals

• UV radiation activates genes involved in melanin synthesis, leading to darker pigmentation (e.g., tanning in humans)

  • Darker pigmentation of the skin protects against DNA damage from UV rays

• Environmental stressors directly influence protective phenotypic traits

Pheromone production in fungi

• Chemical signaling is used by yeast and fungi to identify mating partners

• As yeast cells detect pheromones from the opposite mating type they alter the gene expression and produce complementary pheromones

• This response ensures successful mating and demonstrates the impact of social and chemical environmental cues on genotype expression