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How can several genes contribute to a single trait such as height or eye colour?

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Four kittens with different fur patterns-three tabby and one black-and-white-lying together in a box, illustrating genetic variation among offspring. — heredity Each offspring is a combination of its two parents, receiving some dominant traits from its mother and others from its father.

Traits such as height and eye colour are often influenced by multiple genes, a phenomenon known as polygenic inheritance. Contrary to the once-held belief that such characteristics follow simple Mendelian patterns, they are actually determined by the collective expression of several or many genes, each contributing a small effect to the overall phenotype.123

In polygenic systems, these genes work together to establish a range of variation rather than distinct, binary categories. For example, height is a polygenic trait involving thousands of genetic variations that act as a blueprint for growth, influencing factors like bone length and cartilage development. Similarly, while eye colour was once thought to be simple, it is now understood to be complex, with multiple genes coding for various factors related to pigmentation and iris patterning.243

It is important to note that these genetic factors do not act in isolation. For many polygenic traits, the final outcome is the result of an interplay between heredity and environmental factors, such as nutrition or health, which can influence how fully a genetic potential is realized.542