Incomplete dominance

Definition

Incomplete dominance is a genetic scenario where the phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes. This means that neither allele is completely dominant over the other, leading to a blend of traits in the offspring. This concept is crucial for understanding how traits are inherited and expressed, revealing the complexity of genetic interactions beyond simple dominant-recessive patterns.

5 Must Know Facts For Your Next Test

1. Incomplete dominance can be observed in flower color, such as when red and white snapdragon flowers produce pink offspring.
2. In incomplete dominance, the phenotypic ratio of offspring can often be different from the expected Mendelian ratios due to the blending effect.
3. The concept of incomplete dominance challenges the classical Mendelian inheritance model, showing that not all traits follow simple dominant and recessive patterns.
4. In plants, incomplete dominance can lead to a variety of flower colors and shapes, affecting pollination and survival strategies.
5. This form of inheritance is important in plant breeding and genetics, as it can produce diverse phenotypes that may have adaptive advantages.

Review Questions

• How does incomplete dominance differ from complete dominance in terms of phenotypic expression?
  • Incomplete dominance differs from complete dominance because, in incomplete dominance, the heterozygote exhibits a blended phenotype that is intermediate between the two homozygous phenotypes. For example, when red and white flowers cross, the offspring might show pink flowers instead of expressing only one of the parental colors. This blending highlights that neither allele fully masks the other, unlike complete dominance where one allele completely overshadows the other.
• Discuss an example of incomplete dominance in a real-world scenario and its implications on trait variation.
  • An example of incomplete dominance can be found in certain species of snapdragons, where crossing red and white flowers results in pink flowers. This blending illustrates how genetic interactions can produce new phenotypic variations that may impact plant reproduction and survival. In this case, it can also affect pollinator behavior and plant attractiveness, demonstrating how incomplete dominance influences ecological relationships.
• Evaluate how incomplete dominance contributes to our understanding of inheritance patterns and its relevance in modern genetics.
  • Evaluating incomplete dominance enhances our understanding of inheritance by illustrating that genetic expression is more complex than traditional dominant-recessive models suggest. It reveals that traits can result from interactions between alleles that lead to blended phenotypes. This understanding is particularly relevant in modern genetics for developing new plant varieties through selective breeding and studying genetic disorders where incomplete dominance might play a role in disease expression.

Related terms

Codominance: A genetic scenario where both alleles in a heterozygote are fully expressed, resulting in a phenotype that displays characteristics of both alleles.

Polygenic Inheritance: A type of inheritance where multiple genes contribute to a single trait, resulting in a wide range of phenotypes.

Genotype: The genetic makeup of an organism, consisting of the alleles inherited from its parents, which can influence its phenotype.