A gene is a specific location on a chromosome that codes for a particular protein. Alleles are variants of a gene that determine how the protein looks.
Every cell in the body contains genetic material in the form of DNA. During times of DNA replication, such as mitosis or meiosis, DNA condenses into chromosomes. Chromosomes also contain protein and RNA that help to regulate DNA function. Most of the DNA in the human body is noncoding and has no discernible function.
For regions of DNA that do code for specific proteins, each particular coding region is a gene. Genes provide instructions for building proteins, and every gene has alternate forms. These alternate forms are alleles. For example, genes code for the production of eye color pigment, while alleles determine the specific amount or color of the pigment. The specific genes that an individual inherits make up that person's genotype, while the visible traits that result from the genes are the individual's phenotype; it is possible for multiple genotypes to result in the same visible traits.
Much of what modern science understands about genetic inheritance is the result of the work of an Augustinian priest called Gregor Mendel. Mendel is responsible for developing an understanding of the genetic contributions of parent organisms to offspring through his work with pea plants.