What is the Difference Between Complementary and Supplementary Genes

The main difference between complementary and supplementary genes is that the complementary genes are two independent genes which interact together to produce a trait but, neither gene can produce their own trait alone whereas the supplementary genes are two independent genes which interact together to produce a trait but, each gene can produce their own traits alone.  

Complementary and supplementary genes are two types of interactions between genes to produce a combined trait. The two genes involved in the interaction are non-allelic and dominant. 

Key Areas Covered 

1. What are Complementary Genes
     – Definition, Independent Traits, Examples
2. What are Supplementary Genes
     – Definition, Independent Traits, Examples
3. What are the Similarities Between Complementary and Supplementary Genes
     – Outline of Common Features
4. What is the Difference Between Complementary and Supplementary Genes
     – Comparison of Key Differences

Key Terms 

Complementary Genes, Dominant, Interaction of Genes, Non-Allelic, Supplementary Genes

What are Complementary Genes 

The complementary genes are a type of non-allelic genes which can interact together to produce a combined trait. Each gene in the complementary pair cannot produce independent traits though they are dominant. As an example, two sweet pea varieties may produce white color flowers in successive generations. But, when the two white flower color varieties are crossed, the F1 generation will produce purple color flowers. However, F2 generation produces both purple and white color flowers in the phenotypic ratio, 9 purple: 7 white. Here, the purple color develops by the combination of two genes which are in the dominant state.  

Figure 1: Red Eye Color in Drosophila

Another example of complementary genes which produce the red-eye in Drosophila is shown in the above diagram. Here, the two complementary genes are A and B. 

What are Supplementary Genes 

The supplementary genes are two non-allelic genes which can produce independent traits. But in combination, they can produce a different trait. As an example, the R gene independently can produce the red color in the grains of maize. However, the homozygous recessive state does not produce a color; hence, the grain color is white. But, in the presence of the dominant P gene, the dominant R gene produces purple grain color. However, same as the recessive r gene, the recessive p gene has no effect on the grain color.  

Figure 2: Different Grain Colors in Maize

The F1 generation of the above cross produces the combined phenotype, which is purple color grains. The F2 generation produces the phenotypic ratio, 9 purple: 3 red: 4 white grains.  

Similarities Between Complementary and Supplementary Genes 

• Complementary and supplementary genes are two types of interactions that can occur while producing combined traits. 
• Both genes involved in these interactions are non-allelic. 
• Also, these genes have to be dominant in order to produce the combined trait. When these genes have no effect, they produce no traits and the phenotype can be white color as an example. 
• The F1 generation of the dominant allele cross shows the combined trait. 
• Furthermore, both types of gene interactions make alterations to the phenotypic ratio of the F2 generation, 9:3:3:1 in the Mendelian inheritance.  

Difference Between Complementary and Supplementary Genes 

Definition 

Complementary genes refer to the genes which complement the effects of each other and the presence of both the genes is essential for the production of wild phenotype while supplementary genes refer to two independent pairs of genes interacting in such a manner that one dominant factor produces its effect whether the other is present or not, while the second gene can produce its effect only in the presence of the first. 

Independent Traits 

The dominant genes in the complementary gene pair cannot produce independent traits while the dominant genes in the supplementary gene pair can produce independent traits, which is different from the combined trait. This is the main difference between complementary and supplementary genes.

Phenotypic Ratio in the F2 Generation 

The phenotypic ratio in the F2 generation is a major difference between complementary and supplementary genes. The phenotypic ratio of the F2 generation in complementary genes is 9:7 while the phenotypic ratio of the F2 generation in supplementary genes is 9:3:4. 

Examples 

Some examples of complementary genes are the purple flower color of the sweet pea and the red eye color in the Drosophila while some examples of the supplementary genes are purple grain color in maize and coat color of the mice. 

Conclusion 

Complementary genes are a type of gene interactions in which the independent gene cannot produce a trait though it is dominant. On the other hand, supplementary genes are another type of gene interactions in which the independent dominant gene in the pair can produce their own trait. Both complementary and supplementary genes are two types of gene interactions which produces a combined trait when the two genes in the pair are dominant. The main difference between complementary and supplementary genes is the ability of the dominant genes to produce their own traits independently.

Reference:

1. Sharma, Aastha. “8 Important Forms of Gene Interactions.” Biology Discussion, 12 July 2016, Available Here

Image Courtesy:

1. “Complementation” By Mcstrother – Own work This vector image includes elements that have been taken or adapted from this:  Drosophila-drawing.svg. (CC BY-SA 3.0) via Commons Wikimedia  
2. “Indian corn 2” By Alessandra Cimatti (CC BY 2.0) via Flickr