Question

skin color in humans has a wide variety of phenotypes. the expression of this trait is caused by more than two genes. what type of inheritance pattern is responsible for this expression?
polygenic inheritance
complete dominance
incomplete dominance
codominance

Explanation:

• Polygenic inheritance: Occurs when a trait is controlled by more than one gene. Each gene contributes a small effect, and together they result in a wide range of phenotypes. Skin color in humans is a classic example of polygenic inheritance as it is influenced by multiple genes.
• Complete dominance: A situation where one allele (the dominant allele) completely masks the effect of the other allele (the recessive allele) in a heterozygous individual. For example, in pea plants, the allele for purple flowers (P) is completely dominant over the allele for white flowers (p). So, a plant with genotype Pp will have purple flowers. This does not explain skin - color variation caused by multiple genes.
• Incomplete dominance: Happens when the heterozygous phenotype is intermediate between the two homozygous phenotypes. For example, in snapdragons, a red - flowered plant (RR) crossed with a white - flowered plant (rr) gives pink - flowered (Rr) offspring. It is a single - gene inheritance pattern (in this case, for flower color) and not related to multiple - gene inheritance of skin color.
• Codominance: Occurs when both alleles in a heterozygous individual are fully expressed. For example, in the ABO blood group system, if an individual has genotype AB, both A and B antigens are expressed on the red blood cells. This is a single - gene (or a few - gene, in the case of blood groups, but still not multiple genes for a single trait like skin color) inheritance pattern.

Answer:

polygenic inheritance