Trait: In genetics, a feature of a living thing is called a trait. Some traits are part of an organism's physical appearance; such as a person's eye-color, height or weight. Other sorts of traits are not easily seen and include blood types or resistance to diseases.
Phenotype: A phenotype is the composite of an organism's observable characteristics or traits, such as its morphology, development, biochemical or physiological properties. Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and their interactions. When two or more clearly different phenotypes exist in the same population of a species, it is called polymorph.
Genotype: The genotype of an organism is the inherited instructions it carries within its genetic code. Not all organisms with the same genotype look or act the same way because environmental factors and developmental conditions result in variation. Likewise, not all organisms that look alike necessarily have the same genotype.
Genotype-Phenotype distinction: This genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911. The distinction is similar to that proposed by August Weismann, who distinguished between germplasm (heredity) and somatic cells (the body).