Differences Between Genotypes & Phenotypes With Examples
DNA, deoxyribonucleic acid, makes up genes. Sexually reproducing organisms usually have two alleles, or versions, of each gene, one inherited from each genetic parent. Genes are arranged into chromosomes. An individual's or species' complete collection of chromosomes is its genome. Genotype is the actual physical DNA carried inside an individual's cells. Phenotype is the observable physical expression of that DNA.
Genotypes express a variety of phenotypes through dominance, polygenic inheritance and pleiotropy, developmental buffering and environmental interaction. Dominance is interaction between alleles in the same gene. Polygenic inheritance and pleiotropy are interactions among different genes. Developmental buffering is when the overall process of normal development prevents certain genotypes from expressing as phenotypes. Environmental interaction is when the same genotype produces different phenotypes under different conditions.
Dominance is also called Mendelian inheritance. Alleles can be dominant, recessive, codominant, or incompletely dominant. A dominant allele in the genotype is always expressed in the phenotype. For example, if brown eye color is dominant in a species, an animal that inherits even a single brown allele will always have brown eyes. If it's recessive, he'll only have brown eyes if he inherits a brown allele from each parent. If it's codominant or incompletely dominant, a brown allele plus another can blend to produce a third eye color, or two differently colored eyes, or eyes with patches of each color.
Polygenic inheritance refers to the situation in which a particular phenotype is controlled by many different genes in different places within the genome. For example, human skin color is polygenic: Different genes at different loci -- places on the chromosomes -- interact to produce a rainbow of possibilities so variable a child's skin color cannot be predicted by looking at his genetic parents. In pleiotropy, on the other hand, one set of alleles controls more than one phenotypic trait. For example, a single allele in cats is dominant for white coat color and pleiotropic with incomplete dominance for blue eye color and degenerative hearing loss.
Developmental buffering, also called developmental canalization, is when many processes in normal embryonic development prevent the expression of certain phenotypes regardless of genotype. For example, Drosophila fruit flies normally have two large eyes plus three ocelli, or mini-eyes, that are arranged in a triangle on top of their heads. Individuals in some Drosophila species carry different alleles for ocelli number. However, under normal circumstances, almost all allele combinations produce a single phenotype -- three ocelli in the correct places.
Environmental interaction can cause the same genotype to express as multiple phenotypes. For example, human height is a polygenic trait expressed differently under different environmental conditions, such as when children with the same height genotype grow to different adult heights -- or phenotypes -- based on differences in early nutrition. Stochastic effects are the result of random, unpredictable environmental hazards. They can also cause a single genotype to express as multiple phenotypes -- for example, when a "skin-cancer-prone" genotype causes light skin in everyone who has it, but only those exposed to certain types of ultraviolet radiation actually develop the cancer.
- National Institutes of Health, Genetics Home Reference: Phenotype
- National Institutes of Health, Genetics Home Reference: Genotype
- Stanford University: The Genotype/Phenotype Distinction
- Indiana University - Purdue University of Indianapolis: Human Genetics - Inherited Disorders and Exceptions to Mendel's Rules
- Estrella Mountain Community College: Gene Interactions
- International Cat Care: Inherited Deafness in White Cats
Angela Libal began writing professionally in 2005. She has published several books, specializing in zoology and animal husbandry. Libal holds a degree in behavioral science: animal science from Moorpark College, a Bachelor of Arts from Sarah Lawrence College and is a graduate student in cryptozoology.