Organisms carry both dominant and recessive alleles of a gene. Such organisms would be called carriers of a recessive allele. In this instance, the organism would only show the dominant phenotype of the gene. Cystic fibrosis is another homozygous recessive phenotype. Other diseases, such as Huntington's, are also expressed through the recessive phenotype. However, individuals with Huntington's have either a mutant-mutant expression or a normal-mutant one.
Homozygous means that the organism contains two copies of the same allele for a particular gene. Homozygous recessive means that the organism carries two recessive alleles. Such as with the example above, the white-flowered pea plant has two white alleles to make it be expressed that way. Carriers of the recessive gene are considered to be heterozygous, meaning they have only one allele of each of the dominant and recessive alleles. Huntington's disease is considered to be autosomal dominant, so an individual with this disease could either have a heterozygous gene or a homozygous dominant one. The genotype is the combination of alleles for a certain gene. The genotypes provide the framework for the phenotype that will be expressed.Learn more about Biology