Genes carry the instructions for producing proteins, which are crucial for determining an organism's traits. These traits can be physical, such as eye color or height, and behavioral, like temperament. Genes exist in various forms called alleles, and combinations of these alleles from both parents influence the expression of traits in offspring. Additionally, environmental factors can also interact with genes, leading to variations in traits among individuals within a species. This complex relationship between genes and traits is fundamental to the study of inheritance and evolution.