Genotypes and Phenotypes

 The genotype is the genetic code of an individual. The phenotype is just the physical expression of the genotype that can be observed by other organisms. While genotype is what is passed down from generation to generation it is the phenotype that selection acts upon. This makes sense as if there was a change to the genotype that did not affect the phenotype, it would not influence that population greatly when it came to successfully reproducing. Acting on phenotype selection induces evolutionary changes due to how successful that phenotype is at reproducing and passing down its genes. Take a butterfly population for example. If there was an evolutionary change in the genotype that did not affect the phenotype, predators would have no reason to stop eating the butterflies. Still, if there was an evolutionary change in the genotype that made the phenotype of the butterfly appear to look venomous then its predators would be less likely to eat them allowing them to reproduce and pass down this evolutionary trait.