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Codominance – Definition, Ratio, Blood Group Example and Facts

What is Codominance?

Codominance is a genetic concept where two different alleles for a gene are both expressed in an organism, and neither dominates over the other. In simpler terms, if you have a gene with two alleles (versions), instead of one allele masking the effect of the other, both alleles show their traits simultaneously. Imagine a flower with a red allele and a white allele for color. In co-dominance, each allele contributes independently to the phenotype without blending.

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This phenotype is often observed in blood type genetics. For example, in the ABO blood group system, an individual with one A allele and one B allele will express both A and B antigens on their blood cells. This dual expression distinguishes co-dominance from incomplete dominance, where the trait may blend. Co-dominance provides genetic diversity, as both alleles maintain their distinct characteristics. It’s like having a mixed playlist where you can hear each song clearly rather than a blend of different tunes. This concept is crucial in understanding the complexity of genetic traits and how various alleles interact to shape the observable features of organisms.

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Example of Codominance – Blood Group

Co-dominance is a genetic concept where two alleles of a gene are both expressed in the phenotype, resulting in a combined, distinguishable trait. An example is the blood type AB in humans. If a person inherits an A allele from one parent and a B allele from the other, both alleles are expressed, leading to the co-dominant AB blood type. Unlike other cases where one allele may dominate, here, both contribute equally. This contrasts with incomplete dominance, where a blend of traits occurs. Co-dominance, where a blend of traits occurs. Co-dominance highlights the simultaneous, distinct expression of multiple alleles, providing genetic diversity and illustrating the complexity of inheritance in a straightforward manner.

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More Examples of Codominance

Codominance occurs when both alleles in a heterozygous individual express their traits fully. These examples illustrate how co-dominance allows for the simultaneous expression of multiple alleles, producing a distinct phenotype that reflects the contribution of both alleles.

  • Roan Cattle Coat Color:
  1. In cattle, the alleles for red coat color and white coat color are co-dominant.
  2. Roan cattle have a coat with a mixture of red and white hairs.
  • Sickle Cell Anemia:
  1. In the case of sickle cell anemia, co-dominance is observed in individuals with one allele for normal cell hemoglobin and one allele for sickle cell hemoglobin.
  2. This results in a condition called sickle cell trait, where both types of hemoglobin are produced.
  • Chicken Feather Color:
  1.  In some chicken breeds, the alleles for black feathers (B) and white feathers (W) are co-dominant.
  2. Heterozygous chickens (BW) display a pattern of both black and white feathers.
  • Flower Color in Snapdragons:
  1. In snapdragons, the alleles for red flower color (R) and white flower color (W) are co-dominant.
  2. Heterozygous individuals (RW) have pink flowers due to the co-expression of both alleles.
  • Horse Coat Color – Appaloosa Pattern:
  1. The Appaloosa pattern in horses is governed by co-dominant alleles.
  2. Horses with one allele for solid color and one for the spotted pattern (Leopard complex) exhibit a blend of both characteristics.

Facts on Codominance Alleles

As we know co-dominance provides a fascinating example of genetic variation, showcasing the simultaneous expression of multiple alleles and contributing to the diversity within a population

  • Co-dominance Definition: Co-dominance is a genetic concept where two different alleles for a gene are expressed independently in a heterozygous individual.
  • Distinct Expression: Unlike incomplete dominance, co-dominance involves both alleles maintaining their distinct characteristics without blending.

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  • Blood Type Example: A classic example is the ABO Blood group system in humans, where the A and B alleles are co-dominant. An individual with an AB genotype expresses both A and B antigens on their red Blood Cells.
  • Genetic Variation: Co-dominance contributes to genetic diversity within a population by allowing for the simultaneous expression of multiple alleles.
  • Heterozygous Individuals: In co-dominance, heterozygous individuals exhibit a phenotype that reflects the presence of both alleles, highlighting the unique expression pattern.

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Codominance: FAQs

Q1. What is Co-dominance?

Ans: Co-dominance means both alleles in a gene pair show their traits, creating a combined phenotype. No dominance, just a mix of both characteristics.

Q2. Give an example of Co-dominance?

Ans: In co-dominance, if you have different traits from your parents, you show a mix of both, like having spots from one parent and strips from the other.

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