Gene Interaction: Overview, Definition, Types, Importance In Evolution

Gene interactions are seen when two or more allelic or non-allelic genes of the same genotype influence the result of certain phenotypic characters. To understand the molecular mechanisms of this phenomenon, there is a requirement for genetic interaction and gene mapping, where the effects on one gene are modified by certain genes. The pairwise deletion of genes or inhibition of gene expression can be utilised to identify genes with similar function.

This Story also Contains

1. What is Gene Interaction?
2. Allelic or Non-Epistatic Gene Interaction
3. Nonallelic or Epistatic Gene Interaction
4. Classification of Epistatic Gene Interaction
5. Recommended video for "Gene Interaction"
6. MCQs on Gene Interaction

Genetic interaction is the functional interaction between genes. One such example is epistasis, the interaction of non-allelic genes, which is the interaction of non-allelic genes where the effect of one gene is masked by another gene. The result is either the suppression of the effect or both of them together produce a new trait. Mapping the genetic interactions gives an idea of how the genes function together. It proves to be a powerful tool for systematically defining gene function and pathways. Gene interactions are an important topic in biology subject.

What is Gene Interaction?

Gene interaction or gene cooperation is defined as the cooperation of genes to regulate the expression and final outcome of an organism’s phenotype. This concept is very important in genetics because it aids in showing how certain traits and diseases are inherited in the human body due to the combination of various genes. They include gene interactions concerning understanding evolution as well as diversification.

Some of the significant forms of gene interactions include

• epistasis- one gene dominates or alters the second gene;

• additive effects- multiple genes contributing to a characteristic/phenotype; and

• pleiotropy- a single gene influences multiple characteristics/phenotypes.

These genes interact with each other and knowledge of these interactions shows the intricacies of genetic control and evolutionary processes.

Types of Gene Interactions

Gene interactions can be subdivided into two categories:

• Allelic or Non-epistatic Gene Interaction: This gene interaction goes on between the alleles of one gene.

• Nonallelic or Epistatic Gene Interaction: This type of gene interaction involves the interaction between genes on identical or different chromosomes.

Allelic or Non-Epistatic Gene Interaction

Allelic interaction is defined as the interaction between alleles at the same gene locus. In non-epistatic interactions, one gene does not suppress another.

Types of Allelic Interactions

The Allelic interactions are classified as:

Complete Dominance

• One allele completely masks the effect of another.

• For example, in garden peas, the tall stem is represented by the allele T, which is dominant to the short allele, t. Thus, the genotypes Tt and TT are both tall in appearance.

Incomplete Dominance

• Here, the heterozygote phenotype is intermediate between the phenotypes of the homozygotes.

• Example: In snapdragons, the allele for red flowers (R) is incompletely dominant over the allele for white flowers (r), producing pink flowers (Rr).

Codominance

• Both alleles are expressed in the heterozygote.

• For example, in cattle, the alleles for red hair (R) and white hair (W) are codominant, producing roan cattle (RW) with both red and white hairs.

Overdominance

• Heterozygote has an advantage over both homozygotes.

• Example: Individuals heterozygous for the sickle cell allele (AS) are resistant to malaria compared to those homozygous for normal haemoglobin (AA) or sickle cell anaemia (SS).

Genotypic and Phenotypic Ratios

• Allele interactions are thus seen to modify Mendelian genetics patterns that deviate from the genotypic and phenotypic ratios of offspring.

• Incomplete dominance and codominance typically produce a 1:2:1 phenotypic ratio in the F2 generation.

Importance in Evolution

• As a result of allelic interaction, populations increase in their genetic diversity and adaptation.

• Overdominance secures a selective advantage for heterozygotes and thus helps maintain genetic variation within a population.

Research and Applications

• The study of allelic interaction gives insight into genetics, breeding, and medicine.

• It creates awareness of breeding in plants and animals by deducing the phenotypic output once genotype combinations are known.

• Under allelic interactions, the study of genetics leading to disorders and the treatment of those disorders through medicine is helped.

Nonallelic or Epistatic Gene Interaction

Epistasis refers to the event of interaction between different genes; the effect of one gene masks or modifies the expression of a second gene. Non-allelic interactions refer to interactions between alleles at different loci.

Methods of Epistatic Interactions

Epistatic interactions are categorised as:

Recessive Epistasis

A recessive allele at one locus masks the effects of alleles at another locus.

Example: In the case of Labrador retrievers, two genes control the coat colour — B and E. Now, the gene E acts as an epistatic for the gene B, such that ee will result in a yellow colour independent of the alleles for the B gene.

Dominant Epistasis

When an allele at one locus is dominant over all alleles at another locus, this can be similar to fruit colour in summer squash.

Example: In summer squash, a dominant allele at one locus acts to mask the expression of the gene for fruit colour. This results in white squash even in the presence of Y.

Duplicate Gene Action

Two genes perform the same function, so a dominant allele at only one of the loci can be sufficient for the expression of the trait.

Example: In some plants, two genes independently act for flower colour. Therefore, in F2 it is due to either A or B that the flower colour appears, which constitutes a 15:1 ratio.

Complementary Gene Action

Two genes complement each other— each contributing what the other lacks—for an organism to produce that phenotype.

Example: Here, two dominant alleles are needed at two loci to have purple flowers in sweet peas. This constitutes an F2 generation ratio of 9:7.

Genotypic or Phenotypic Ratios

Epistasis can shift typical genotypic and phenotypic ratios for a 9:3:3:1 ratio in a dihybrid cross to any other ratio, including 9:3:4, 12:3:1, 15:1, or even 9:7, depending on the type of epistasis.

Significance of Epistatic Genes in Evolution

• Epistatic interactions contribute to genetic complexity and diversity in populations.

• They have the power to influence traits under natural selection, hence the evolutionary pathways and adaptation processes.

Research And Applications

• Epistasis is of importance in genetic research, in particular, in the study of complex traits and diseases.

• It is important in breeding programs for predicting phenotypic outcomes and improving desirable traits in plants and animals.

• In medicine, such epistatic interactions are of key importance for understanding the genetic basis of complex diseases and for the development of better diagnostic and therapeutic strategies.

Classification of Epistatic Gene Interaction

Epistatic gene interaction is categorised based on how the involved genes affect one another’s expression:

• Supplementary Gene Interaction

• Complementary Gene Interaction

• Inhibitory Gene Interaction

• Duplicate Gene Interaction

• Masking Gene Interaction

• Polymeric Gene Interaction

Supplementary Gene Interaction

• In supplementary gene interaction, the phenotypic effect is produced by the dominant allele of any one of the two genes controlling a character.

• The dominant allele of the second gene has no phenotypic effect alone, but it can modify the effect of the first gene when both dominant alleles occur together.

• Example: Agouti (grey) coat development in mice.

• F2 Ratio: 9 Agouti : 3 Coloured: 4 Albino.

Complementary Gene Interaction

• Complementary gene interaction occurs when two genes producing the same phenotype when they are homozygous result in only one phenotype in the heterozygous state.

• Interaction occurs in the presence of both kinds of dominant alleles to produce a different kind of phenotype.

• Example: Flower colour in sweet peas.

• F2 Ratio: 9:7 instead of 9:3:3:1.

• Mechanism: Both dominant alleles must be present for the expression of the phenotype; their absence does not produce the phenotype.

Inhibitory Gene Interaction

• Inhibitory gene interaction occurs when a dominant allele at one locus inhibits the expression of alleles at another locus.

• There is no distinction in phenotype between the heterozygous and homozygous dominant forms of the inhibitory gene.

• Example: Feather colour in chickens.

• F2 Ratio: Changes from 9:3:3:1 to 13:3.

• Mechanism: A dominant allele is an inhibitor of another gene, producing a unique phenotype only in the homozygous recessive condition.

Duplicate Gene Interaction

• Duplicate gene interaction is an interaction between two gene loci, either of which, when homozygously dominant, produces the same phenotype, and there is no cumulative effect.

• Example: The shape of the seed capsule of Shepherd's purse

• Ratio in F2: Modified into 15:1 ratio from 9:3:3:1

• Mechanism: Both genes produce the same phenotype except when both are homozygous recessive, and the phenotype is the ovoid capsule.

Masking Gene Interaction

• Masking gene interaction occurs when the dominant allele of one gene masks the activity of the allele of another gene.

• Example: Fruit colour in summer squash.

• F2 Ratio: Dominant epistatic relationships where the dominant allele expresses itself no matter what the alleles are for the other gene.

• Mechanism: The allele of the epistatic locus expresses itself unless the epistatic locus is homozygously recessive.

Polymeric Gene Interaction

• Polymeric gene interaction is when two dominant alleles in genes act together to enhance a phenotype or create a medium-type phenotype.

• Example: Colour of kernels in wheat.

• F2 ratio: 9:6:1, and other ratios show the combined effect.

• Mechanism: Both dominant alleles are of an equal degree in the expression of phenotype; therefore, it enhances or leads to a medium-type phenotype.

Recommended video for "Gene Interaction"

MCQs on Gene Interaction

Q1. Duplicate genes, supplementary genes, and polymorphic genes can be grouped under:

Option 1: Gene interaction

Option 2: Linkage

Option 3: Recombination

Option 4: Maternal effect

Correct answer: (1) Gene interaction

Explanation:

The phenomenon of two or more genes influencing each other's expression in different ways during the evolution of a single organismal characteristic is known as gene interaction. Dominant epistasis, supplemental gene interaction, complementary factor, polymorphic gene, and duplicate gene activity are among the gene interaction types that can be investigated.

Hence, the correct answer is option (1) Gene interaction.

Q2. When a gene suppresses or masks the expression of another gene, it is said to be an

Option 1: Hypostatic gene

Option 2: Recombination

Option 3: Epistatic gene

Option 4: Linkage

Correct answer: (3) Epistatic gene

Explanation:

Epistatic Gene: When a gene suppresses or masks the expression of another gene, it is said to be an epistatic gene.

Hypostatic Gene: The gene which is suppressed by the epistatic gene is called the hypostatic gene.

Hence, the correct answer is option (3) Epistatic gene

Q3. What is the difference between allelic and non-allelic interactions?

Option 1: Allelic interactions occur between genes on the same chromosome, while non-allelic interactions occur between genes on different chromosomes.

Option 2: Allelic interactions involve the interaction between alleles of the same gene, while non-allelic interactions involve the interaction between genes that are not alleles.

Option 3: Allelic interactions are only observed in prokaryotic organisms, while non-allelic interactions occur in eukaryotic organisms.

Option 4: Allelic interactions are always dominant, while non-allelic interactions can be either dominant or recessive.

Correct answer: (2) Allelic interactions involve the interaction between alleles of the same gene, while non-allelic interactions involve the interaction between genes that are not alleles.

Explanation:

Allelic interactions refer to the interactions between different versions of the same gene, which are called alleles. These alleles may be different versions of the same gene due to mutations or genetic variation. Allelic interactions can result in dominant or recessive patterns of inheritance.

On the other hand, non-allelic interactions involve the interactions between genes that are not alleles. These genes may be located on different chromosomes or different regions of the same chromosome. Non-allelic interactions can result in a variety of phenotypic outcomes, such as epistasis, where one gene can affect the expression of another gene, or complementation, where two genes are required for a specific phenotype to be expressed.

Hence, the correct answer is option (2) Allelic interactions involve the interaction between alleles of the same gene, while non-allelic interactions involve the interaction between genes that are not alleles.

Also Read:

• Practice MCQs on Gene Interaction

• Lethal Genes

• Human Genetic Disorders