IB Biology Topic D3.2.6: Phenotypic Plasticity Notes

Phenotypic Plasticity Changes Traits Without Changing the Genes

1. Organisms adjust to their environment through phenotypic plasticity, which changes traits without altering the genetic code.
2. The genes provide the blueprint, but the environment shapes the final outcome.

Environmental Cues Switch Genes On and Off

1. Plasticity works by turning genes on or off in response to environmental cues.
2. Unlike a mutation, these changes are often temporary and reversible.
3. The environment influences gene expression, which controls the proteins made and the traits they shape.
4. Human tanning
   1. Sunlight raises melanin production, darkening the skin to protect against UV rays, and it fades again when sun exposure drops.

1. Aquatic plant leaves
   1. Submerged leaves grow narrow to cut water resistance, while floating leaves grow broad to capture more sunlight.

Plasticity Differs From Genetic Change

Two Types of Plasticity: Reversible and Developmental

1. Reversible plasticity: short-term changes such as tanning or fur thickness that adjust to passing conditions.
2. Developmental plasticity: traits fixed during early life, such as a tree's canopy shape set by sunlight and wind, which then stay permanent.

Plasticity Has Limits and Costs

1. Not all changes are reversible: developmental changes are fixed for life, even though no gene has been altered.
2. Energy costs: constantly adjusting in a rapidly changing environment can use a lot of energy, reducing the benefit.

Plasticity and the Idea of Evolution