Co-Dominance and Incomplete Dominance

Review of Basic Genetic Concepts

• Homozygous: Individual with the same two alleles for the same trait.
• Heterozygous: Individual with different alleles for the same trait.
• Dominant and Recessive Alleles: Dominant allele masks the presence of a recessive allele in the phenotype.
• Complete Dominance Example:
  • Blood type: A allele is dominant over O allele.
  • Genotype AO results in phenotype A because A is completely dominant over O.

Patterns of Dominance

Complete Dominance

• Definition: Only the dominant allele in the genotype is expressed in the phenotype.
• Example: Flower with genotype Red (R) and Blue (r), if R is dominant over r, the phenotype will be a red flower.

Co-Dominance

• Definition: Both alleles in the genotype are fully expressed in the phenotype.
• Example: Flower with some red petals and some blue petals under co-dominance conditions.

Incomplete Dominance

• Definition: Neither allele is completely dominant, resulting in a mixture of the two alleles being expressed.
• Example: Flower with genotype Red (R) and Blue (r), the phenotype will be a purple flower (mixture of red and blue).

Summary

• Complete Dominance: Dominant allele is seen in the phenotype, e.g., Red flower.
• Co-Dominance: Both alleles are seen in the phenotype, e.g., Flower with both red and blue petals.
• Incomplete Dominance: A mixture of the alleles is seen in the phenotype, e.g., Purple flower.