Final answer:
Alternate forms of genes resulting from mutations are called alleles. Mutations can result in different forms of genes and can affect a person's phenotype. In Huntington's disease, a dominant lethal allele, individuals who are heterozygous for the disease allele will develop the fatal disease.
Step-by-step explanation:
Alternate forms of genes resulting from mutations are called alleles. Mutations are changes in the sequence of DNA nucleotides that can result in different forms of genes. These mutations can affect a person's phenotype, which is the observable characteristics or traits of an individual. For example, in Huntington's disease, a dominant lethal allele, individuals who are heterozygous for the disease allele will develop the fatal disease. The disease may not manifest until adulthood, but it can be unknowingly passed on to offspring.