The table below lists five basic genetic terms, with one definition left blank.

Term	Definition
Chromosome	A thread-like structure made of DNA, found in the nucleus, carrying many genes
Gene	A section of DNA on a chromosome that codes for a particular characteristic
Allele	One of two or more alternative versions of a gene
Genotype	The particular combination of alleles present in an organism for a given characteristic
?	The observable physical or biochemical characteristics of an organism, resulting from the interaction of its genotype with the environment

Which term is represented by the question mark in the table?