A phenotype is the set of traits or characteristics of an organism that can be directly seen or measured by scientific methods. It comes from the combination of the organism's genetic makeup (genotype) and its environment.
These traits include physical features, how the organism develops, its biochemical and physiological functions and its behaviors. Some phenotypes are easy to notice, such as height or eye color, while others are more subtle, such as blood type or hormone levels.
Populations usually have many different phenotypes because of genetic differences and varying environmental conditions. Environmental factors that affect phenotypes include temperature, humidity, sunlight, oxygen levels, nutrition, exposure to mutagens, and social interactions. These factors can change how genes are expressed without altering the actual genetic code itself.
Larger populations tend to have greater phenotypic and genetic diversity than smaller ones because they have less inbreeding and are less affected by random genetic changes. This diversity is important because it helps populations adapt to changing environmental conditions.