Genetic material is the medium by which instructions are transmitted from one generation of organisms to the next. In life on Earth, it takes the form of nucleotide sequences that are organized into genomes. A genome is all of the DNA contained within the cell of a living being. Each molecule of human DNA has billions of nucleotides arranged like steps on a ladder.
It's the sequence of nucleotides that determines the traits of the organism. At various places, called loci, along each chromosome between large stretches of non-coding, DNA sequences of nucleotides resolve into coherent patterns that instruct messenger proteins in how to build other proteins. These proteins are synthesized in the cytoplasm of the cell and work to build every structure of a living body. Genes, as a natural consequence of their nucleotide sequences, build proteins, and proteins build bodies.
Genetic material is passed among large organisms by vertical transmission from parent to offspring. Each offspring resembles its parent more closely than it resembles a randomly chosen member of its species because the exact sequence of genetic instructions on how to build the body have been inherited from the parent. Small errors in copying genes are known as mutations, and their proliferation throughout a gene pool drives the process of evolution.