Genetics
Pleiotropy
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When a single gene affects multiple phenotypic traits. Changes to pleiotropic genes have cascading effects throughout the organism—the genetic basis of 'everything is connected to everything.'
Biological Context
Pleiotropy occurs when one gene influences multiple phenotypic traits, creating genetic trade-offs. The sickle cell allele both causes sickle cell disease AND provides malaria resistance. Pleiotropy constrains evolution because mutations beneficial for one trait may be harmful for others—natural selection must optimize packages of traits, not individual traits. This explains why organisms seem 'stuck' with certain trait combinations that appear suboptimal when viewed in isolation.