Other alleles are dominant or recessive to the wild type allele. An individual can have two copies of the same allele or two different alleles. Hereditary cases involve an inherited mutation and a single mutation in the normal allele. These lineages are unable to reproduce sexually due to being homozygous for a recessive allele. This meant that each opposite parent was homozygous for its respective allele only. Dominance is not inherent to an allele or its traits (phenotype). "q" is the fraction homozygous for the alternative allele. This ultimately caused gene fixation of the Adh1 wild type allele. Another example of a recessive lethal allele occurs in the Manx cat. FOP is caused by an autosomal dominant allele on chromosome 2q23-24. Their whitish fur is a rare morph caused by a double recessive allele. The allele for yellow pods is recessive. This was the first documented example of a recessive lethal allele. Specifically, it is the fraction of all chromosomes in the population that carry that allele. Roan is a simple dominant trait symbolized by the "Rn" allele.