Incomplete dominance

Definition

Incomplete dominance is a genetic phenomenon where the phenotype of a heterozygote is an intermediate blend of the phenotypes of the homozygous individuals. This means that neither allele is completely dominant over the other, resulting in a third phenotype that reflects a mix of both traits. This concept expands on traditional Mendelian genetics by demonstrating that inheritance can be more complex than simple dominant and recessive relationships.

5 Must Know Facts For Your Next Test

1. In incomplete dominance, the phenotype ratio in offspring from a cross between two homozygotes typically results in a 1:2:1 ratio among the three phenotypes.
2. One classic example of incomplete dominance is seen in snapdragon flowers, where crossing red (RR) and white (WW) flowers produces pink (RW) offspring.
3. Incomplete dominance challenges the traditional Mendelian view by showing that traits can blend rather than being determined solely by dominant alleles.
4. This type of inheritance plays a role in various species and can have implications for plant breeding and animal husbandry.
5. In incomplete dominance, the expression of both alleles does not result in complete masking; instead, it highlights how phenotypic expression can vary with environmental factors.

Review Questions

• How does incomplete dominance differ from complete dominance in terms of phenotype expression?
  • Incomplete dominance differs from complete dominance as it results in an intermediate phenotype in heterozygotes, whereas complete dominance leads to one trait being fully expressed over the other. In incomplete dominance, both alleles contribute to the phenotype, blending their effects to create a new trait. For example, crossing red and white flowers can yield pink flowers in incomplete dominance, while in complete dominance, one color would completely overshadow the other.
• Discuss an example of incomplete dominance and explain its significance in understanding genetic inheritance.
  • A classic example of incomplete dominance is found in snapdragon plants, where crossing red-flowered plants with white-flowered ones produces pink-flowered offspring. This observation is significant as it illustrates how not all traits follow simple Mendelian inheritance patterns. It shows that alleles can interact in ways that lead to novel phenotypes, highlighting the complexity of genetic inheritance beyond just dominant and recessive traits.
• Evaluate the implications of incomplete dominance for fields such as agriculture and genetics research.
  • The implications of incomplete dominance for agriculture are profound, as understanding this genetic mechanism allows breeders to create new plant varieties with desired characteristics by exploiting trait blending. In genetics research, studying incomplete dominance enhances our understanding of gene interactions and how phenotypes are influenced by multiple alleles. This knowledge contributes to advancements in genetic engineering and biotechnology, allowing for more targeted approaches to crop improvement and disease resistance.

Related terms

codominance:

A genetic scenario where both alleles in a heterozygote are fully expressed, resulting in offspring with a phenotype that shows both traits distinctly.

allele:

Different forms of a gene that can exist at a specific locus on a chromosome, influencing the traits of an organism.

phenotype:

The observable physical and physiological traits of an organism, which result from the interaction of its genotype with the environment.