Codominance

Definition

Codominance is a genetic phenomenon where both alleles in a heterozygote are fully expressed, resulting in offspring with a phenotype that shows both traits simultaneously. This concept highlights how inheritance can be more complex than simple dominance, allowing for multiple traits to manifest in the presence of different alleles.

5 Must Know Facts For Your Next Test

1. In codominance, neither allele is dominant or recessive; instead, both are expressed equally in the phenotype.
2. A classic example of codominance is seen in the ABO blood group system, where individuals with genotype IAIB express both A and B antigens on their red blood cells.
3. Codominance can be differentiated from incomplete dominance, where the traits blend together rather than being fully expressed.
4. This genetic pattern plays an important role in population genetics and can influence genetic variability within a species.
5. Understanding codominance helps explain certain inherited conditions and traits that do not follow simple Mendelian inheritance patterns.

Review Questions

• How does codominance differ from other inheritance patterns such as dominance and incomplete dominance?
  • Codominance differs from simple dominance in that both alleles are fully expressed in the phenotype of heterozygotes, rather than one allele masking the other. In contrast, incomplete dominance results in a blended phenotype where neither allele is fully expressed. An example illustrating codominance is seen in blood types, where individuals with both A and B alleles express both antigens without blending them.
• Describe how codominance contributes to genetic diversity within populations and provide an example.
  • Codominance contributes to genetic diversity by allowing multiple traits to be expressed simultaneously within individuals. This creates a broader range of phenotypes in a population, enhancing adaptability. A prime example is the ABO blood group system, where individuals can have multiple blood types due to the presence of codominant alleles (IA and IB), leading to diverse immune responses and compatibility in transfusions.
• Evaluate the implications of codominance on understanding human genetics and inherited diseases.
  • The implications of codominance on human genetics are significant as it challenges traditional Mendelian models of inheritance. It enhances our understanding of inherited traits and conditions that arise from multiple allelic expressions. For instance, certain genetic disorders may exhibit codominant traits, necessitating comprehensive genetic counseling and testing strategies that consider all possible allele combinations, improving diagnosis and treatment approaches for affected individuals.

Related terms

allele:

An allele is a variant form of a gene that can occupy the same position on a chromosome, contributing to genetic diversity.

incomplete dominance:

Incomplete dominance occurs when the phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes, unlike codominance where both traits are fully expressed.

multiple alleles:

Multiple alleles refer to the existence of more than two allelic forms for a particular gene within a population, such as blood types A, B, AB, and O.