Dominance, Incomplete Dominance and Codominance – Lesson Summary

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Learning Objective

In this lesson we will learn about the three modes of biological inheritance – dominance, incomplete dominance and codominance.

Learning Outcomes

By the end of this lesson you will be able to:

Describe the three modes of biological inheritance:

Dominance

Incomplete dominance

Codominance

Define ‘dominant’ and ‘recessive’ in terms of alleles and phenotypes.

Write genotypes for dominance, incomplete dominance and codominance.

Predict phenotypes of homozygotes and heterozygotes for dominance, incomplete dominance and codominance.

dominance incomplete dominance and codominance lesson contents

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Lesson Summary

There are three main modes of inheritance – dominance (dominant and recessive inheritance), incomplete dominance and codominance.

These vary by how alleles contribute to the phenotype, in particular, how the phenotype of heterozygotes is determined.

When dominance occurs, one allele (the dominant allele) is dominant over the other (the recessive allele).

Heterozygotes will have the dominant phenotype.

When incomplete dominance or codominance occurs, neither allele is dominant over the other.

For incomplete dominance, heterozygotes will have an intermediate phenotype.

For codominance, heterozygotes will have a combination of phenotypes.

For dominant and recessive inheritance, dominant alleles are represented by uppercase letters and recessive alleles are represented by lowercase letters.

For incomplete dominance and codominance, alleles are represented by different uppercase letters.

dominant recessive alleles genotype

(Image: GraphicsRF, Adobe Stock)

(Header image: htrnr, Adobe Stock)