The key difference between additive and nonadditive genetic patterns is based on the effect that it created on the phenotype. In additive genetic patterns, both alleles contribute to the phenotype in measurable amounts, while in nonadditive genetic patterns, only one allele contributes to the phenotype through dominance or epistasis.
Both additive and nonadditive genetic patterns belong to the study of quantitative behavioural genetics as the contributions of the interaction are measurable. Both of these scenarios are important in giving rise to variations in populations.
CONTENTS
1. Overview and Key Difference
2. What are Additive Genetic Patterns
3. What are Nonadditive Genetic Patterns
4. Similarities Between Additive and Nonadditive Genetic Patterns
5. Side by Side Comparison – Additive vs Nonadditive Genetic Patterns in Tabular Form
6. Summary
What are Additive Genetic Patterns?
Additive genetic patterns arise as a result of the interaction between alleles of the same gene. This interaction decides the final phenotype of an organism. Therefore, in additive genetic patterns, both alleles have an effect on the final phenotype. Thus, the phenotype will be a result of the total effect of the two alleles that are interacting. The alleles can be placed in one or more gene loci. The amount at which each allele contributes to the final phenotype may vary. Therefore, the combinations resulting from the additive genetic patterns may vary widely.
What are Nonadditive Genetic Patterns?
Nonadditive genetic patterns are a result of interactions between genes. These interactions may take place in the same locus or at different loci. Based on this, nonadditive genetic patterns can take place through phenomena called dominance or epistasis.
Dominance is the effect when the interaction takes place at the same loci. In this scenario, one allele is dominant above the other. The phenotype will be based on the characteristic imparted by the dominant allele. In both homozygous dominant condition and heterozygous condition, the dominant allele will be expressed. The recessive allele will be expressed only if it is in the homozygous recessive condition.
Figure 02: Nonadditive Genetic Pattern
Epistasis is the other type of nonadditive genetic pattern. In this pattern, the interactions take place at different loci, and the phenotype is produced in a nonadditive pattern. In this phenomenon, the effect of one allele is altered by the second allele to produce a nonadditive genetic pattern. Nonadditive genetic patterns can be seen when determining human hair colour and determination of baldness.
What are the Similarities Between Additive and Nonadditive Genetic Patterns?
- In both additive and nonadditive genetic patterns, there is an interaction between genes or alleles.
- Both give rise to variation in populations.
- Both belong to the study of quantitative behavioural genetics.
What is the Difference Between Additive and Nonadditive Genetic Patterns?
The key difference between additive and nonadditive genetic patterns is the way in which allele interactions take place. In additive genetic patterns, both alleles contribute to the phenotype in measurable amounts, while in nonadditive genetic patterns, only one allele contributes to the phenotype through dominance or epistasis.
Below infographic tabulates the differences between additive and nonadditive genetic patterns.
Summary – Additive vs Nonadditive Genetic Patterns
Additive and nonadditive genetic patterns explain the quantitative genetics of organisms. Additive genetic patterns arise due to the additive effects of both alleles in a gene in measurable varying amounts. In contrast, nonadditive genetic patterns explain the effect of a single allele on the phenotype through dominance or epistasis. Thus, this is the key difference between additive and nonadditive genetic patters. However, both patterns give rise to variation in organisms and populations.
Reference:
1. Hahn, Elisabeth. “Additive and Nonadditive Genetic Patterns.” SpringerLink, Springer, Cham, 1 Jan. 1970, Available here.
2. Waldmann, Patrik. “Additive and Nonadditive Genetic Architecture of Two Different-Sized Populations of Scabiosa Canescens.” Nature News, Nature Publishing Group, 1 June 2001, Available here.
Image Courtesy:
1. “Epistatic hair” By Thomas Shafee – Own work (CC BY 4.0) via Commons Wikimedia