Gene interaction is an important topic in NEET Biology. This NCERT-focused guide explains epistasis, pleiotropy and polygenic inheritance in a simple and exam-oriented way. It includes important examples, comparison tables, mnemonics and practice MCQs to help students prepare for NEET Biology 2027.
Quick Answer: Gene Interaction
Gene interaction occurs when the expression of one gene is influenced or modified by another gene or genes. Therefore, the expression of a trait may depend on interactions among several genes rather than on a single gene acting independently.
- Epistasis: One gene masks or modifies the expression of another gene.
- Pleiotropy: One gene affects multiple traits.
- Polygenic inheritance: Multiple genes contribute to one trait.
In This Guide
- What is Gene Interaction?
- Epistasis
- Types of Epistasis
- Pleiotropy
- Polygenic Inheritance
- Difference Between Epistasis, Pleiotropy and Polygenic Inheritance
- Important Examples for NEET
- NEET Biology Quick Revision
- Practice MCQs
- NEET Preparation Tips
1. What Is Gene Interaction?
Gene interaction refers to the phenomenon in which the expression of one gene is influenced or modified by another gene or by several other genes.
In simple Mendelian inheritance, a single gene pair may determine a particular character. However, many biological traits involve interactions between genes. These interactions can modify the expected Mendelian ratios and produce different phenotypic patterns.
Gene interaction does not necessarily mean that genes physically interact. It generally refers to the way the expression of one gene affects the phenotype produced by another gene.
2. Epistasis — One Gene Masks Another
Epistasis is a type of gene interaction in which one gene masks or modifies the expression of another gene.
The gene whose expression is masked is called the hypostatic gene, while the gene that produces the masking effect is called the epistatic gene.
Easy Way to Remember
Epistasis = External Power Influence
One gene influences the expression of another gene.
Types of Epistasis — Quick Comparison
| Type | Basic Idea | Common Example |
|---|---|---|
| Dominant epistasis | A dominant allele at one locus can mask expression at another locus. | Summer squash fruit colour |
| Recessive epistasis | A homozygous recessive genotype at one locus masks another gene. | Coat colour in Labrador retrievers |
| Duplicate recessive epistasis | Recessive alleles at either of two loci can prevent the phenotype. | Flower colour in sweet pea |
3. Pleiotropy — One Gene, Many Effects
Pleiotropy occurs when a single gene influences multiple phenotypic traits.
Therefore, one gene may produce effects in several different body systems or biological characteristics.
Easy Mnemonic
Pleiotropy = Plenty Effects
One gene → multiple effects.
Important Examples of Pleiotropy
| Gene / Condition | Multiple Effects |
|---|---|
| HbS allele | Can be associated with sickle-cell anaemia in homozygous individuals and other effects related to malaria resistance in heterozygotes. |
| Phenylketonuria | A metabolic defect can have effects including impaired mental development and other physiological changes when untreated. |
| Marfan syndrome | A genetic disorder that can affect connective tissues and produce effects in the skeleton, eyes and cardiovascular system. |
4. Polygenic Inheritance — Many Genes, One Trait
Polygenic inheritance occurs when a single trait is controlled by two or more genes.
Each contributing gene may have an additive effect, producing continuous variation in the phenotype.
Important Examples
- Human skin colour — influenced by multiple genes.
- Human height — influenced by many genetic and environmental factors.
- Some quantitative traits show continuous variation.
💡 NEET Tip
Polygenic inheritance usually produces a range of phenotypes rather than a simple dominant-versus-recessive pattern. Environmental factors may also influence quantitative traits such as height.
5. Difference Between Epistasis, Pleiotropy and Polygenic Inheritance
| Concept | Genes Involved | Main Idea | Mnemonic |
|---|---|---|---|
| Epistasis | Two or more genes | One gene masks or modifies another | Gene → Gene |
| Pleiotropy | One gene | One gene affects several traits | One → Many |
| Polygenic inheritance | Many genes | Many genes contribute to one trait | Many → One |
6. One-Minute Revision
Epistasis: One gene masks or modifies another gene.
Pleiotropy: One gene affects multiple traits.
Polygenic inheritance: Multiple genes influence one trait.
Remember:
- Epistasis → Gene affects gene
- Pleiotropy → One gene, many effects
- Polygenic inheritance → Many genes, one trait
7. Important Examples for NEET Biology
- Summer squash fruit colour: Example associated with dominant epistasis.
- Labrador coat colour: Example commonly used to explain recessive epistasis.
- Sweet pea flower colour: Classic example of complementary gene interaction / duplicate recessive epistasis.
- Sickle-cell anaemia: Useful example when discussing pleiotropic effects of a gene.
- Phenylketonuria: An important example of pleiotropy.
- Human skin colour: Classic example used to explain polygenic inheritance.
8. Gene Interaction MCQs for NEET Biology 2027
1. When one gene masks the expression of another non-allelic gene, the phenomenon is called:
A. Pleiotropy
B. Epistasis
C. Polygenic inheritance
D. Mutation
✅ Answer: B. Epistasis
2. Pleiotropy refers to:
A. One gene affecting one trait only
B. One gene affecting multiple traits
C. Many genes affecting no traits
D. One allele masking another allele
✅ Answer: B. One gene affecting multiple traits
3. Polygenic inheritance occurs when:
A. One gene controls many traits
B. One gene masks another
C. Multiple genes contribute to one trait
D. A chromosome is duplicated
✅ Answer: C. Multiple genes contribute to one trait
4. Which of the following is an example commonly associated with recessive epistasis?
A. Labrador coat colour
B. Human blood group only
C. Haemophilia only
D. Turner syndrome
✅ Answer: A. Labrador coat colour
5. Human skin colour is commonly used as an example of:
A. Pleiotropy
B. Polygenic inheritance
C. Recessive epistasis
D. Sex-linked inheritance
✅ Answer: B. Polygenic inheritance
6. Which statement correctly describes pleiotropy?
A. Many genes determine one trait
B. One gene masks another gene
C. One gene influences several phenotypic traits
D. One chromosome determines all traits
✅ Answer: C. One gene influences several phenotypic traits
7. In epistasis, the gene that masks the expression of another gene is called the:
A. Hypostatic gene
B. Epistatic gene
C. Recessive gene only
D. Linked gene
✅ Answer: B. Epistatic gene
8. The gene whose expression is masked by an epistatic gene is called:
A. Epistatic gene
B. Hypostatic gene
C. Mutant gene
D. Pleiotropic gene
✅ Answer: B. Hypostatic gene
9. Which relationship is correctly matched?
A. Epistasis — One gene, many traits
B. Pleiotropy — Many genes, one trait
C. Polygenic inheritance — Many genes, one trait
D. Pleiotropy — One gene masks another
✅ Answer: C. Polygenic inheritance — Many genes, one trait
10. Which of the following best represents pleiotropy?
A. One gene → multiple effects
B. Multiple genes → one quantitative trait
C. One gene → one protein only
D. One allele → one chromosome
✅ Answer: A. One gene → multiple effects
9. How to Prepare Gene Interaction for NEET
For NEET Biology, do not try to memorize isolated definitions. First understand the direction of the relationship.
Step 1: Read the relevant NCERT Biology concepts.
Step 2: Learn the difference between epistasis, pleiotropy and polygenic inheritance.
Step 3: Memorize the important examples.
Step 4: Practise MCQs without looking at the answers.
Step 5: Revise mistakes repeatedly.
NEET Biology for Odisha Students
Students preparing for NEET in Odisha can use this NCERT-focused Biology resource for concept revision and MCQ practice. A strong Biology strategy should focus on understanding NCERT concepts, practising questions and regularly revising difficult topics.
Whether you are preparing through self-study or coaching, use these questions as part of your regular NEET Biology 2027 revision routine.
10. Test Yourself
Try answering all the MCQs without checking the answers.
- 9–10 correct: Excellent concept clarity.
- 7–8 correct: Good preparation; revise weak areas.
- 5–6 correct: Revisit the concepts and examples.
- Below 5: Read the topic again from NCERT and practise once more.
11. Final Takeaway
Gene interaction is easier to remember when the three major concepts are kept separate:
Epistasis: One gene affects the expression of another gene.
Pleiotropy: One gene produces multiple phenotypic effects.
Polygenic inheritance: Multiple genes contribute to one trait.
For NEET Biology preparation, focus on the definitions, examples, comparisons and question patterns. Regular revision is more useful than trying to memorize too many disconnected facts.
📚 Related NEET Biology Resources
➜ Class 11 Biology — NCERT Notes
➜ Cell Biology MCQs for NEET
➜ Cell Cycle and Cell Division — NEET Biology
➜ Genetics and Evolution — NEET Biology
➜ NEET Biology Resources for Odisha Students
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