Gene interactions and eugenics

Polygenic inheritance

Trait controlled by multiple genes (e.g., height, skin color); shows continuous variation.

Penetrance

Probability that a gene will be expressed in individuals who carry it.

Expressivity

Degree or intensity with which a trait is expressed.

Delayed onset

Genetic trait appears later in life (e.g., Huntington’s disease).

Pleiotropy

One gene affects multiple traits (e.g., sickle-cell anemia).

Epistasis

One gene masks or modifies the effect of another gene.

Continuous variation

Traits that show a full range of values (e.g., height, weight).

Discontinuous variation

Traits with clear categories (e.g., blood type, attached earlobes).

Eugenics

Movement aiming to improve the human species by selective breeding or restricting reproduction.

Ethical issues of eugenics

Led to forced sterilizations and discrimination; rejected by modern genetics.

Modern view on eugenics

Promotes diversity, equality, and ethical responsibility in genetic research.