Incomplete Dominance, Codominance, and Linkage – NEET Genetics Simplified

🌸 Incomplete Dominance

In incomplete dominance, neither allele is completely dominant, and the heterozygote shows a blend of the two traits.

🧪 Example: Snapdragon flower color

Genotype Phenotype

RR Red

rr White

Rr Pink ← Blended

🧠 NEET Trick: “Incomplete = Intermediate”

📌 Phenotypic ratio = Genotypic ratio = 1:2:1

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🧬 Codominance

In codominance, both alleles express equally in the heterozygote. There’s no blending.

🧪 Example: AB Blood Group

IA and IB are codominant

IAIB genotype → Blood Group AB (both A and B expressed)

🧠 NEET Tip: “Co = Coexist”

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🔗 Linkage

Linkage is the tendency of genes located close together on the same chromosome to be inherited together.

📌 Law of Independent Assortment Fails Here

Genes on the same chromosome do not assort independently if they are tightly linked.

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🔍 Types of Linkage

Type Description Example

Complete No crossing over between linked genes Male Drosophila

Incomplete Some recombinants seen due to crossing over Female Drosophila

🧠 NEET Tip: “Closer the genes = Stronger the linkage”

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🌱 NEET Summary Table

Concept Key Idea Example

Incomplete Dominance Blended phenotype Pink Snapdragon

Codominance Both alleles express AB blood group

Linkage Genes inherited together Drosophila traits