If the phenotype shows a recessive mutation, it is double on the inside (homozygous genotype). If it's a dominant mutation on the outside (phenotype), it can be homozygous or heterozygous (only one (of two) Alele) caries the mutation. For Example: wildtype homozygous (AA) Wildtype het. Albino (Aa)
(sorry for my bad English

I'm sure there is someone who can explain it better as I do)