John and Pat are denticle twins with identical DNA John works in a movie theater in pat works as a lifeguard they have very different pigmentation which is the best explanation of the difference

Skin color, a polygenic trait, is also determined by environmental factors.

Explanation:

In humans, skin color or pigmentation is a polygenic trait and is also determined by environmental factors such as exposure to the sun.

Polygenic traits are the traits which are controlled by two or more genes located on different chromosomes. For example, height, skin color, and color of the eyes.

John and Pat carry identical DNA however they exhibit different interaction of the polygenes and working conditions (environmental factors). For example, John works in a movie theatre and thus does not have much exposure to sun whereas Par works on the beach which is an open area and thus experience a lot of exposure from the sun.  

Exposure to the sun leads to the darker skin and thus polygenic interactions and different environmental conditions lead to the variation in skin pigmentation in John and Pat.

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