What describes variations not always observable as phenotypic variations?

Genotypic variations refer to the differences in the genetic makeup of individuals within a population. These variations can affect traits, but they are not always immediately observable in the physical characteristics (phenotypes) of those individuals. For example, two individuals may have different genotypes that could lead to the same phenotypic expression or might result in traits that do not manifest due to environmental factors or recessive alleles. This highlights how genotypic variations play a fundamental role in the diversity of traits within a species, but the connection to observable traits is not always direct or obvious.

In contrast, the other choices pertain to specific genetic processes or concepts that do not directly address variations that conceal themselves at the phenotypic level. Gene flow refers to the transfer of genetic material between populations; Mendelian variations describe inheritance patterns based on Mendel's laws, focusing on observable traits; gene migration involves the movement of genes across populations but does not specifically address variation at the genotype level. Thus, the focus on the genetic basis of traits makes genotypic variations the most fitting description of variations not always observable as phenotypic variations.