A mutated gene is a gene that has undergone a change in its DNA sequence, resulting in a different form of the gene. An allele is one of two or more forms of a gene that can exist at a particular locus on a chromosome. Alleles can be either dominant or recessive, and they can be responsible for different traits in an organism. Mutated genes can cause genetic disorders, such as cystic fibrosis, sickle cell anemia, and Huntington's disease.