What term refers to the observable traits of an organism?

The term that refers to the observable traits of an organism is phenotype. The phenotype encompasses all the physical characteristics and observable features of an organism, such as color, shape, size, and behavior, resulting from the interaction between its genotype (the genetic makeup) and the environment.

For example, in a plant species, the height, flower color, and leaf shape can be considered as part of the plant's phenotype. This concept highlights the expression of genes in the context of the organism's environment, which determines how those genes are manifested in physical traits.

The other terms mentioned relate to genetics but focus on different aspects. Genotype refers to the genetic constitution of an organism, specifically the alleles it possesses. Karyotype involves the number and appearance of chromosomes in the nucleus of a cell, which provides insight into genetic disorders and chromosomal structures but does not directly describe observable traits. Alleles are the different versions of a gene that can exist at a particular locus, which contribute to the genotype that ultimately influences the phenotype.