The types of genes can be initially classified as heterozygous mutations and pure mutations. The type of gene is determined by whether the ribonucleic acids on both chromosomes are identical. If the ribonucleic acids on both chromosomes are normal, the genotype is normal. If one ribonucleic acid on both chromosomes is normal and the other is mutated, the genotype is a heterozygous mutation. If the ribonucleic acid is abnormal on both chromosomes, the genotype is a pure mutation. Some genetic heterozygous mutations cause hearing loss and some genetic heterozygous mutations cause normal hearing. Most genotypes that are purely heterozygous mutations will cause hearing loss.