Phenotype
The phenotype is the observable set of physical and biochemical characteristics of an organism, resulting from the interaction of its genotype with the environment. It encompasses all visible traits such as eye colour, height, blood type, and behavioural tendencies. Understanding phenotype is fundamental to genetics because it reveals how genetic information is expressed in living organisms.
Examples of Human Phenotypic Traits and Their Categories
| Trait | Phenotype Examples | Controlled By | Environmental Influence |
|---|---|---|---|
| Eye colour | Brown, blue, green, hazel | Multiple genes | Minimal |
| Blood type | A, B, AB, O | ABO gene (single locus) | None |
| Height | Tall, average, short | Polygenic | Nutrition, health |
| Skin colour | Range of pigmentation | Multiple genes | Sun exposure |
| Tongue rolling | Can roll / cannot roll | Single gene | Minimal |
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Related Terms
Genotype
Genotype refers to the complete genetic constitution of an organism — specifically, the set of alleles present at a given locus or across all loci in the genome. Unlike phenotype (the observable characteristics), genotype is the underlying inherited sequence information that, in combination with environmental influences, determines the traits of an organism. Determining genotype is fundamental to genetic counselling, disease risk assessment, and molecular breeding programmes.
Dominant Allele
A dominant allele is a version of a gene whose trait is expressed in the phenotype whenever at least one copy is present, regardless of whether the other allele is the same or different. Dominant alleles are conventionally represented by uppercase letters (e.g., "B" for brown eye colour). The concept of dominance was first described by Gregor Mendel through his experiments on pea plants in the 1860s.
Heterozygous
An organism is heterozygous for a particular gene when it carries two different alleles at that genetic locus — one dominant and one recessive (e.g., Aa). The dominant allele is expressed in the phenotype, while the recessive allele is carried but not expressed, making the individual a "carrier" of the recessive trait. Heterozygosity is important in population genetics because it maintains genetic diversity and affects the probability of recessive disorders appearing in offspring.
From Greek "phainein" meaning "to show" or "to appear", combined with "typos" meaning "type" or "impression". The term was introduced by Danish botanist Wilhelm Johannsen in 1911 to distinguish observable traits from underlying genetic composition.