Originally Posted by
Flashball
The statement that "genotype and phenotype are not correlated" is largely incorrect, depending on the context in which it is made.
Genotype vs Genome
It's important to distinguish between the "genotype" and the "genome." The genome encompasses the complete set of an individual's genetic material. The genotype, on the other hand, often refers to a more limited set of genetic variations relevant to a specific trait or set of traits. For example, the specific alleles you have for a gene determining eye color constitute a genotype for that particular trait.
In the context of commercial genetic tests like 23andMe, the term "genotype" can be misleading. These tests only cover about 0.2% of an individual's genetic variations, making it more appropriate to talk about the genome as a whole rather than the genotype when discussing the basis for various traits and characteristics.
Correlation between Genotype and Phenotype
The correlation between genotype and phenotype can vary depending on the trait in question and its heritability. For traits that are strictly genetic, like certain monogenic diseases (caused by mutations in a single gene), the link between genotype and phenotype is very strong. For complex polygenic traits influenced by multiple genes and also by environmental factors (like height or intelligence), the relationship is more nuanced but still present.
The Impact of the Environment
The environment can also play a significant role in the expression of phenotype. For instance, two plants with the same genotype can have different phenotypes if one is grown in full sun and the other in shade.
Conclusion
Thus, it's incorrect to say that genotype and phenotype are not correlated. They are generally correlated, but the strength of this correlation can vary considerably depending on a range of factors, including environmental impact and the complexity of the trait in question. The phenotype is, in a way, a complex manifestation of the genome.