Gene Interaction: Epistasis, Pleiotropy & Polygenic Inheritance – NEET Simplified

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🌱 1. What is Gene Interaction?

Gene interaction means one gene’s expression is modified by one or more other genes. It is beyond simple Mendelian (monogenic) inheritance.


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🔄 2. Epistasis – Gene Masks Another Gene

Definition:
When one gene suppresses (masks) the expression of another non-allelic gene, it's called epistasis.

Type of Epistasis Description Example

Dominant Epistasis Dominant allele masks another gene Fruit color in summer squash
Recessive Epistasis Recessive allele (homozygous) masks another Coat color in Labrador retrievers
Duplicate Recessive Two recessive genes needed for a trait Flower color in sweet pea


🧠 Mnemonic:
“Epistasis = External Power Influence” (One gene influences another)


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🧬 3. Pleiotropy – One Gene, Many Effects

Definition:
When a single gene affects multiple traits, it's called pleiotropy.

Gene Trait Affected Example

HbS gene (Sickle cell) RBC shape, malaria resistance, anemia Sickle-cell anemia
PKU gene Mental development, skin pigment Phenylketonuria
Marfan’s syndrome Skeleton, eyes, heart FBN1 gene on chromosome 15


🧠 Mnemonic:
“Pleiotropy = Plenty Effects” (One gene, many symptoms)


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🌾 4. Polygenic Inheritance – Many Genes, One Trait

Definition:
When multiple genes control a single trait, it is called polygenic inheritance.

Trait Inheritance Example

Height Continuous (bell curve) 3–6 genes involved
Skin color Additive effect of alleles At least 3 gene pairs
Eye color Multiple genes Not binary dominant/recessive


🧠 Mnemonic:
“Polygenic = Pile of Genes” (Many genes = one trait)

✅ Key Features:

Shows continuous variation

No clear-cut ratios (unlike Mendelian)

Environmental effect plays a role



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🔁 Summary Table

Concept Genes Involved Trait Affected NEET Hint

Epistasis 2+ genes 1 trait 9:3:4 or 12:3:1 ratios
Pleiotropy 1 gene Multiple traits One mutation = many symptoms
Polygenic Many genes 1 trait Height/skin color shows curve

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