Genotype & Phenotype Definition

By Daniel Zimmermann
The color, size and shape of flowers depend on the plant's genotype.
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Genotype and phenotype come from the Greek. The word “typos" can designate a pattern, a model or an image. The word “genos” can mean the kind of thing something is or the race to which someone belongs. Various forms of the verb “phaino” describe such actions as showing or appearing. These etymological roots hint at the meanings of genotype and phenotype and outline the differences between them.

Genes

Organisms reproduce after their kind, and they impart to their offspring important chemical units called genes. Such creatures as cows, oak trees and human beings inherit two sets of genes, one set from each parent. Alleles are two genes that correspond to one another in function. One allele comes from each parent.

Definition of Genotype

The genotype of an organism is the sum total of all the genes that it inherits. It is a pattern or a sort of blueprint that is designed to serve as a guide in the development of the organism, so that it will become the same kind of creature as the parent or parents from which it came. On a cellular level, the genotype is the blueprint that guides the cell’s development and activities. It is passed on to the daughter cells when the cell divides.

Definition of Phenotype

The phenotype of an organism includes such factors as its physical appearance, the biochemical processes that take place in its body and its behavior as it lives in the world and interacts with other organisms. In short, the phenotype of an organism is the appearance it presents to observers.

Genotype vs. Phenotype

The genotype of an organism is the dominant factor in its development. Creatures that inherit a turtle genotype always become turtles, and plants that inherit the dogwood genotype always become dogwoods. However, environmental factors also play a role in growth and development. If the head or feet of a baby are bound or tied during their formative years, these members will not develop according to plan. Such sicknesses as cirrhosis of the liver will drastically alter the phenotype of the sufferer. Nor can genotype completely control behavior. Environment is crucial in the development of a person’s personality.

Application to Alleles

The garden pea studied by Mendel inherits a specific allele coding for seed color from each parent plant. Some of these alleles code for yellow seeds, others for green. In this case, the genotype is the alleles and their coded information, while the phenotype is the actual color of the seeds produced. When the two alleles contain the same information, the genotype regularly expresses itself in the corresponding phenotype. However, if a plant inherits one allele coded for yellow seeds and another coded for green, only the allele coded for yellow will be expressed in the phenotype. All the seeds will be yellow.