Humber Admissions Practice Test

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What is the main factor in determining an organism's phenotype?

The environment in which it lives
The organism's genotype
The number of alleles
The mutations it carries

The correct answer is: The organism's genotype

The primary factor that determines an organism's phenotype is its genotype, which encompasses the specific genetic makeup inherited from its parents. The genotype includes the alleles for various traits and can considerably influence how these traits manifest in the organism. The phenotype is the observable characteristics of an organism, such as its physical appearance, behavior, and biochemical properties, which are a result of the expression of the genotype in a given environment. While environmental factors can influence the extent and way a phenotype is expressed, it is the genetic composition that fundamentally dictates the potential traits the organism can have. Understanding the relationship between genotype and phenotype is crucial. For example, two organisms may have the same environmental conditions, but variations in their genotypes will lead to different phenotypes. Therefore, while factors like environmental influences and mutations can play a role in shaping an organism's traits, they do so in conjunction with the underlying genotype, which serves as the blueprint for those traits.