Incomplete dominance

Definition

Incomplete dominance is a genetic phenomenon where the heterozygous phenotype is distinct and often intermediate between the two homozygous phenotypes. This results in a blending of traits, rather than one trait completely masking the other. The concept helps to understand the genetic interactions in inheritance patterns, especially in cases involving multiple alleles and variations in traits.

5 Must Know Facts For Your Next Test

1. In incomplete dominance, the phenotype of the heterozygote is a mix of the phenotypes of the two homozygotes, like red and white flowers producing pink offspring.
2. This blending effect can lead to a greater variety of traits within a population, impacting natural selection and evolutionary processes.
3. Incomplete dominance can complicate pedigree analysis, as the traits may not follow traditional Mendelian ratios seen with complete dominance.
4. It highlights the importance of gene interactions, as the expression of one allele can influence the expression of another.
5. Understanding incomplete dominance is crucial for fields like agriculture and medicine, where trait selection and genetic implications are significant.

Review Questions

• How does incomplete dominance differ from complete dominance and codominance in terms of phenotype expression?
  • Incomplete dominance differs from complete dominance because the heterozygous phenotype is an intermediate blend of the two homozygous phenotypes, whereas in complete dominance, one allele completely masks the other. In codominance, both alleles are fully expressed without blending. For example, red and white flowers can produce pink offspring through incomplete dominance, while codominance would show both red and white patches on flowers.
• Discuss how incomplete dominance can influence genetic diversity and evolutionary processes in a population.
  • Incomplete dominance can lead to increased genetic diversity by allowing for more varied phenotypes within a population. This blending of traits may provide new combinations that enhance adaptability to changing environments. As these varied phenotypes compete for survival, natural selection can favor certain traits over others, impacting evolutionary trajectories and shaping populations over time.
• Evaluate the implications of incomplete dominance for pedigree analysis and its relevance in genetic counseling.
  • Incomplete dominance presents unique challenges for pedigree analysis since the expected Mendelian ratios do not apply directly. This can complicate predictions about trait inheritance, making it harder for genetic counselors to assess risks for offspring based on family history. Understanding these patterns is essential for accurate interpretations and providing informed guidance regarding genetic conditions that may exhibit incomplete dominance.

Related terms

Codominance: A form of inheritance where both alleles in a heterozygote are fully expressed, resulting in offspring with a phenotype that is neither dominant nor recessive.

Multiple Alleles: Refers to a gene that has more than two allelic forms, contributing to variations in traits among a population.

Phenotype: The observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences.