Incomplete dominance

Definition

Incomplete dominance is a genetic phenomenon where the phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes. This means that when an individual inherits different alleles for a trait, neither allele is completely dominant over the other, resulting in a blending effect. This concept challenges the traditional Mendelian view of complete dominance, showing that inheritance can result in a spectrum of traits rather than just dominant and recessive categories.

5 Must Know Facts For Your Next Test

1. Incomplete dominance results in offspring with a phenotype that is a mix of both parental traits, like red and white flowers producing pink flowers.
2. This genetic pattern can be seen in various species, including plants and animals, demonstrating the diversity of inheritance mechanisms.
3. Incomplete dominance is often used to illustrate concepts in genetics because it clearly shows how traits can blend rather than simply showing dominance or recessiveness.
4. In plants, this phenomenon can impact flower color, leaf shape, and other traits, influencing breeding practices in agriculture.
5. It is essential to distinguish incomplete dominance from codominance, where both alleles are fully expressed in the phenotype, like in blood types.

Review Questions

• How does incomplete dominance illustrate the blending of traits in offspring?
  • Incomplete dominance illustrates the blending of traits because when a heterozygous organism is formed from two homozygous parents with different traits, the resulting phenotype is an intermediate form. For example, if a red flower (RR) and a white flower (WW) are crossed, the offspring (RW) will display pink flowers. This blending shows that neither allele is completely dominant over the other, emphasizing that traits can merge to create new expressions.
• Compare and contrast incomplete dominance and codominance, providing examples of each.
  • Incomplete dominance and codominance are both forms of non-Mendelian inheritance but differ in how alleles express themselves. Incomplete dominance results in an intermediate phenotype, like pink flowers from red and white parents. Codominance, on the other hand, occurs when both alleles are fully expressed simultaneously in the phenotype, such as AB blood type where both A and B alleles are present. Understanding these differences helps clarify the complexities of genetic inheritance beyond simple dominant-recessive relationships.
• Evaluate the significance of incomplete dominance in understanding genetic variation within populations.
  • Evaluating incomplete dominance highlights its importance in understanding genetic variation within populations as it showcases how phenotypic diversity arises from various allele combinations. This blending effect contributes to evolutionary adaptability by allowing organisms to exhibit a range of traits that may enhance survival in changing environments. By recognizing how incomplete dominance operates alongside other genetic mechanisms, such as complete dominance and codominance, researchers can better comprehend the complexity of heredity and its implications for biodiversity and evolution.

Related terms

Allele: An alternative form of a gene that can exist at a specific locus on a chromosome, influencing the expression of a particular trait.

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

Homozygous: An organism that has two identical alleles for a particular gene, which can lead to either a dominant or recessive phenotype.