The statement that best describes which traits are expressed by an organism is A.
An organism expresses all the traits for which it carries genes. This is because an organism's traits are determined by the combination of genes it carries, which includes both dominant and recessive genes. Even if a trait is not expressed in an organism, it can still be carried in its genes and passed on to its offspring. Therefore, all the traits for which an organism carries genes have the potential to be expressed in either the organism or its offspring.