The phenotype of an organism is its observable characteristics. It develops from the organism's genome and from the way the genome interacts with the environment. The genes set what is possible, and the environment affects how far that is achieved. A plant with genes for tall growth will stay short if it has too little light or too few minerals. A person's height depends on their genes and on their diet while growing.
Variation can be discontinuous or continuous. In discontinuous variation the characteristic falls into separate groups with no in-between values. Eye colour and blood group are examples, and they are mainly controlled by genes.
In continuous variation the characteristic can take any value in a range between two extremes. Height and weight are examples. They are affected by many genes and also by the environment, such as diet and exercise. Graphs of continuous variation usually show a smooth curve with most individuals near the middle.
