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What is the difference between genotype and phenotype?

Genotype is used in a few different ways, but generally refers to an individual's genetic composition. We can refer to someone’s genotype at a particular SNP - that is, which version of the SNP the individual has.

Example: Your genotype at the SNP that determines earwax type is TT.

We can also refer to an individual's overall genotype, i.e. all the different versions of SNPs/genes an individual possesses across the entire genome.

Example: Your genotype influences the way you look, how you respond to different drugs, and how likely you are to develop certain conditions.

You may also see genotype used as a verb. In this case, it refers to the process of determining which versions of SNPs/genes an individual possesses.

Example: With today's technology, people can be genotyped at 1,000,000 SNPs in a single run.

Phenotype refers to the physical and behavioral characteristics of an individual, such as height, hair color, blood pressure, or whether the individual has hemophilia or perfect pitch. Your phenotype is influenced by both your genes and your environment. For some traits, such as freckles, genes play a large role. But even for this trait, the environment - specifically, exposure to sun - influences the number and location of freckles. For many traits, however, the environment plays a dominant role. For example, although a number of genes appear to influence one’s susceptibility to type 2 diabetes, the rising rates in certain parts of the world reflect changes in lifestyle, namely less healthy diets and reduced physical activity.

Remember that your phenotype can be influenced by both genes and environment, and that many phenotypic traits are the result of the interplay between multiple genes. For example, multiple genes and multiple variants of these genes interact to determine eye color. This means that even though you may have a genotype indicating you are more likely to have brown eyes, your eyes could easily be blue. Your genotype does not determine your phenotype in this case; it provides one clue to what it is more likely to be.

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