What is the observable characteristic of an organism called?

The observable characteristic of an organism is referred to as its phenotype. This term encompasses the physical appearance, behavior, and biochemical properties of an organism that result from the interaction between its genotype (the genetic makeup) and the environment. For example, the color of a flower, the shape of a leaf, or the presence of a particular trait, such as freckling in humans, are all phenotypic expressions. Phenotypes can be influenced by numerous factors, including the organism's genetic information and various environmental conditions.

In contrast, the genotype refers specifically to the genetic constitution of an organism and does not account for the traits that are visibly expressed. The karyotype describes the number and appearance of chromosomes in the nucleus, which provides information about the organism's chromosomal makeup but not directly about observable traits. Alleles are different forms of genes that can influence specific traits, but they do not define observable characteristics on their own without considering the phenotype.