Final answer:
Genes with multiple effects at different life stages or conditions are known as pleiotropic genes, distinct from polygenic traits where several genes contribute to a single phenotype.
Step-by-step explanation:
Genes that have multiple effects at different times in the life span or under different conditions are known as genes with pleiotropic effects. Pleiotropy occurs when a single gene influences multiple phenotypic traits. This is different from polygenic inheritance, which refers to a single trait that is controlled by more than one gene. An example of pleiotropy could be a gene that affects both hair color and susceptibility to a particular disease.
Additionally, traits like skin color and height are often influenced by polygenic traits, where multiple genes contribute to a common phenotype. The combined effects of these genes, along with environmental factors, lead to the wide variability observed in these traits.
Gene expression itself is regulated at various levels, including epigenetic, transcriptional, and translational stages, which can alter how genes impact the organism throughout different stages of life or under varying conditions.