People are genetically different from each other in many ways, including in how many copies each person carries of genes called the rDNA. Dr. Morton published a study in Genetics using the microscopic roundworm C. elegans as a model to explore the effects of changing the number of rDNA copies an individual has.
Morton E. A., Hall A. N., Cuperus J. T., and Queitsch, C. (March 2023). Substantial rDNA copy number reductions alter timing of development and produce variable tissue-specific phenotypes in C. elegans. Genetics. https://doi.org/10.1093/genetics/iyad039