Get complete dominance

The expression of the mutated allele with respect to the normal allele can be characterized as dominant, co-dominant, or recessive. There are five basic modes of inheritance for single-gene diseases: autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, and mitochondrial.

Complete dominance is a condition wherein the allele regarded as dominant completely masks the effect of the allele that is recessive. This is the opposite of codominance. For example, people with blood type A have antigen A. This allele is designated IA.

There are three different types of dominance that are important to understand for the MCAT – complete dominance, incomplete dominance, and codominance. Figure 1 shows the difference between complete and incomplete dominance.

Explanation: Mendelian or complete dominance is a relationship of genes in which one allele of a gene pair that codes for a trait expresses itself over the other allele of the gene pair.

Complete dominance is a condition wherein the dominant allele completely masks the effect of the recessive allele; consequently, both alleles must be recessive for the recessive allele to be expressed.

In complete dominance, only one allele in the genotype is seen in the phenotype. In codominance, both alleles in the genotype are seen in the phenotype. In incomplete dominance, a mixture of the alleles in the genotype is seen in the phenotype.