Final answer:
Two genes differ because they have different DNA sequences, are located at different chromosomal positions, may sort independently during meiosis, and may be expressed differently across cell types, all contributing to genetic diversity and variation in traits.
Step-by-step explanation:
Genes differ from each other because they have different DNA sequences, are found at different chromosomal locations (loci), may assort independently during meiosis, and can be expressed in different cell types. The base sequence of DNA in a gene determines its unique function and characteristics, which leads to variations in traits such as blood type with possibilities like AA, BB, OO, or AB.
Genes located on the same chromosome may be linked and inherited together, while those on different chromosomes assort independently due to the random alignment of chromosomes during meiosis, a concept central to Mendel's law of independent assortment. Moreover, even within the same organism, gene expression can vary between different types of cells, contributing to the functional diversity of tissues and organs.