Non-Mendelian Inheritance
Many traits do not follow a simple dominant-versus-recessive pattern. This lesson extends Mendelian ideas by showing how alleles can interact, how several genes can shape one trait, and how one gene can influence several outcomes.
Learning goals
- define the central terms precisely
- connect molecular, organismal and population evidence
- apply the ideas to unfamiliar biological cases
Core concepts
In incomplete dominance, the heterozygous phenotype is intermediate between the two homozygous phenotypes.
In codominance, both different alleles are fully expressed in the heterozygous phenotype.
A multiple-allele system has more than two allele forms in a population, although one individual still carries at most two.
Polygenic inheritance occurs when many genes contribute to one trait, often creating continuous variation.
Pleiotropy occurs when one gene influences several distinct features of an organism.
Epistasis is an interaction in which an allele of one gene changes or masks the phenotypic effect of another gene.
Concept map
Why these ideas matter
These concepts help scientists interpret evidence, design fair tests, communicate uncertainty, and make responsible decisions in research, health, agriculture, and environmental management.