Phenotype refers to the observable characteristics of an organism – including physical, behavioural and physiological traits

• When two or more clearly different phenotypes exist within a population, the distinctive variants are called polymorphisms

Phenotype may determined by an organism's genetic makeup (genotype) or environmental influences – although most traits result from a combination of both factors

• Genotype only: Human examples include blood type, eye colour and certain genetic conditions (such as haemophilia)
  

• Environment only: Human examples include learned behaviours, cellular traumas (such as frostbite) and certain infectious diseases (such as leprosy)
  

• Combination: Human examples include skin coloration, height, weight and certain metabolic conditions (such as diabetes)
  

Phenotypic Plasticity

Phenotypic plasticity describes how environment and genetics may interact to develop characteristics suited to particular conditions

• It is the capacity for an organism to alter their features in response to environmental triggers by varying patterns of gene expression

Freshwater snails demonstrate plasticity in their shell structure according to their exposure to predator fish (such as the bluegill sunfish)

• Snails form a shell by constructing an organic matrix upon which minerals (like calcium) are deposited – this is called biomineralisation

• Snails with smaller and more rotund shells are more crush-resistant and better protected from predation (less exposure)

• In the presence of predator fish, freshwater snails may alter the shell structure by chainging the expression patterns of biomineralisation

Other examples of phenotypic plasticity include changing breeding or birthing patterns based on environmental conditions and changing the amounts of foliage in plants in response to levels of sunlight

Phenotypic Plasticity