What Are Some Examples of Complete Dominance in Genetics?

Examples of human traits that exhibit complete dominance in their genetic inheritance are free versus attached earlobes, straight versus curved thumbs and second toe length, explains University of Northern Iowa. Free earlobes, straight thumbs and second toes longer than the first toe are all completely dominant traits.

Complete dominance occurs when a trait follows Mendelian genetic rules, meaning that one allele, or version of the gene for a trait, is dominant with another version being recessive, explains College of DuPage. If an individual inherits either a dominant allele from each parent or one dominant allele and one recessive allele, the dominant trait is expressed. In cases where organisms inherit one dominant allele and one recessive allele, the presence of the dominant allele prevents the recessive allele from being expressed if the trait exhibits complete dominance. The recessive trait is expressed only if an organism inherits two recessive alleles, one from each parent.

An individual who has two of the same alleles for a trait is said to be homozygous, while a heterozygote possesses two different alleles, notes University of Washington. When a trait exhibits complete dominance, it is impossible to determine if an individual with the dominant trait is a homozygote or heterozygote by simply looking at the individual, explains College of DuPage. Since free earlobes are dominant, a person with free earlobes may be either a homozygote or heterozygote for the trait. However, someone with attached earlobes is homozygous recessive for the earlobe attachment gene.