What is the genetic model?

• A. Phenotype equals genotype only
• B. Phenotype equals environment only
• C. Phenotype equals random
• D. Phenotype = genotype (total effect of all genes) + environment (everything non-genetic)

Answer: (D)

Phenotype reflects what an organism looks like or how it behaves as a result of both its genetic makeup and its environment. The standard way to express this in breeding and quantitative genetics is that phenotype equals the total genetic effect plus the environmental effect: P = G + E. Here, G stands for the combined effect of all genes across the genome (additive, dominance, and epistatic interactions), while E includes all non-genetic influences like nutrition, management, climate, health, and measurement factors. Sometimes a G×E term is considered to capture situations where gene effects change with the environment, but the baseline model is the sum of genetic and environmental contributions. This makes the chosen option the best because it accurately encapsulates both sources that shape a trait. The other statements ignore one of these essential components or treat phenotype as random, which doesn’t align with how genes and environment jointly determine traits.