When one gene controls two or more different characters simultaneously, the phenomenon is called

The phenomenon in which a single gene influences two or more distinct phenotypic characters is called pleiotropy. In classic genetics, pleiotropy explains cases where mutation or variation at one locus produces multiple, apparently unrelated traits — for example, a single gene affecting seed coat color as well as flower and axil pigmentation in Mendel’s material is attributed to pleiotropy [1]. Contemporary definitions emphasize that one genetic variant can affect multiple traits via independent biological pathways or mediated effects, and pleiotropic loci are widely observed across organisms and traits in genetic studies [2]. Other options (apomixis, polyploidy, polyteny) refer to different phenomena and do not describe one gene affecting multiple characters.

Sources

1. [1] https://www.nature.com/scitable/topicpage/pleiotropy-one-gene-can-affect-multiple-traits-569/
2. [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC2975297/