Environmental Effects on Phenotype

  • Whenever you see a wide range in phenotype (i.e. human height and weight) it’s due to the environment (and/or polygenetic inheritance)
  • Phenotypic plasticity - the ability of a single genotype to produce different phenotypes in different environments
  • Plastic phenotypes are evolutionarily favored over non-plastic phenotypes
    • This can represent evolutionary changes in response to the environment - ex) gray tree frog tadpoles can change both their behavioral and physical phenotypes based on whether or not they live in water filled with predators
    • Tadpoles sensing predator presence become more active, develop a deeper tail to quickly escape, the tail is also larger and often red to encourage predators to strike at the tail (can grow back) vs. the body (fatal)
  • another ex) snowshoe hares respond to changes in their environment (shortening days and colder temperatures meaning winter is coming) and they grow white fur for camouflage, vs growing brown fur in the summer
  • Common example in questions: reptilian sex determination is partially determined by temperature - ZW genotype is always female, but ZZ genotype can develop into male or female based on temp @ which egg is incubated
    • Environmental sex determination allows species to favor male or female offspring based off of which is less abundant in a population to allow for equal mating
  • Some genotypes respond to the environment more drastically than others
    • ex) different strains (genotypes) of corn have very different growth responses to varying levels of nitrogen enrichment in soil - one is barely affected at all, while another increases growth drastically
  • [[When talking about environmental effects on phenotype, always mention FITNESS! Alterations in phenotype often involve fitness tradeoffs - questions will often involve the fact that adaptations in response to environmental changes are good in the moment, but keeping the change in phenotype once the environmental change is gone is often a waste of energy and resources - the organism is more fit without the change[[
  • Twin studies can determine the effect genetics vs. environment has on a phenotype - identical twins have the exact same genes, so any difference in their phenotype must be due to the environment