Final answer:
A gene is a section of a chromosome that codes for a specific trait, with alleles being different versions of these genes, leading to variation in the traits exhibited.
Step-by-step explanation:
A section of a chromosome that contains genetic information for one trait is known as a gene. Genes are specific nucleotide segments located on chromosomes that code for proteins, which in turn determine our traits, such as hair color or blood type. Homologous chromosomes are pairs of chromosomes in a diploid organism that are the same length and have genes at the same locations or loci. However, different versions of a gene, called alleles, can exist and contribute to the variations observed in traits. For example, the gene for blood type has three different alleles: A, B, and O, and the combination of alleles inherited from our parents determines our blood type.