Question

john and pat are identical twins with identical dna. john works in a movie theater, and pat works as a lifeguard. they have very different skin pigmentation. which is the best explanation of the difference?
skin color, a polygenic trait, is also determined by environmental factors.
skin color, a polygenic trait, is also determined by the sex of the individual.
skin color, a trait that demonstrates incomplete dominance, is also determined by environmental factors.
skin color, a trait that demonstrates incomplete dominance, is also determined by the sex of the individual.

Explanation:

Skin color is a polygenic trait (controlled by multiple genes). Identical twins (John and Pat) have the same DNA (same genetic makeup for skin - color - related genes). However, Pat (lifeguard) is exposed to more sunlight (an environmental factor) than John (movie - theater worker). Sunlight exposure can increase melanin production (affecting skin pigmentation). So, the difference in their skin pigmentation is due to the fact that skin color (a polygenic trait) is also influenced by environmental factors.

• The sex of the individual is not relevant here as they are twins (assumed same - sex unless stated otherwise, and even if not, the main difference is due to environmental exposure).
• Skin color is a polygenic trait, not a trait that demonstrates incomplete dominance. Incomplete dominance is when the heterozygous phenotype is intermediate between the two homozygous phenotypes (e.g., snapdragon flower color: red \(RR\), white \(rr\), pink \(Rr\)). Skin color is controlled by multiple genes and is also affected by the environment.

Answer:

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