Claim: Huntington's disease is a disorder that may be inherited.

A gene -LRB- from ancient Greek : γόνος , gonos -RRB- is a locus -LRB- or region -RRB- of DNA which is made up of nucleotides and is the molecular unit of heredity . The transmission of genes to an organism 's offspring is the basis of the inheritance of phenotypic traits . These genes make up different DNA sequences called genotypes . Genotypes along with environmental and developmental factors determine what the phenotypes will be . Most biological traits are under the influence of polygenes -LRB- many different genes -RRB- as well as gene -- environment interactions . Some genetic traits are instantly visible , such as eye color or number of limbs , and some are not , such as blood type , risk for specific diseases , or the thousands of basic biochemical processes that comprise life .   Genes can acquire mutations in their sequence , leading to different variants , known as alleles , in the population . These alleles encode slightly different versions of a protein , which cause different phenotypical traits . Usage of the term `` having a gene '' -LRB- e.g. , `` good genes , '' `` hair colour gene '' -RRB- typically refers to containing a different allele of the same , shared gene . Genes evolve due to natural selection or survival of the fittest of the alleles .   The concept of a gene continues to be refined as new phenomena are discovered . For example , regulatory regions of a gene can be far removed from its coding regions , and coding regions can be split into several exons . Some viruses store their genome in RNA instead of DNA and some gene products are functional non-coding RNAs . Therefore , a broad , modern working definition of a gene is any discrete locus of heritable , genomic sequence which affect an organism 's traits by being expressed as a functional product or by regulation of gene expression .