The genes in each of the billions of organisms found throughout the Earth have one central, overriding function: to perpetuate themselves, not just today, not just tomorrow, not just next year but forever and ever. Genes are DNA: deoxyribonucleic acid. A single gene is a short segment of DNA that activates or controls one or more traits of an organism. It might be helpful to add a few terms often encountered in the gene world: Genome. The complete set of genes in an organism. The human genome has around 20,000 to 25,000 genes Genotype. The genes in each of the billions of organisms found throughout the Earth have one central, overriding function: to perpetuate themselves, not just today, not just tomorrow, not just next year but forever and ever. Genes compete with each other for dominance within an organism’s genome. Genetic kinship, established through reproductive sex, can and usually does generate life-supportive behavior toward parental offspring and other relatives.