BiologyChapter 12: Inheritance
Incomplete Dominance and Codominance — Incomplete
Neither allele hides fully.
Learning objectives
- Define incomplete using accurate biology terms.
- Explain why incomplete matters within incomplete dominance and codominance.
- Apply the learning unit to an FBISE-style example, comparison, diagram, or calculation.
Definition
Neither allele hides fully. 1 : 2 : 1 of three phenotypes. Do not call pink a 'mix of paint' in a chemistry way; it is gene expression. Snapdragon: RR = red, rr = white, Rr = pink (blend). Phenotype ratio 1:2:1 matches genotype ratio — unlike complete dominance where heterozygote looks dominant. This page separates the idea from the wider topic “INCOMPLETE DOMINANCE AND CODOMINANCE” so it can be revised and assessed on its own.
Mathematical form
RR = red
rr = white
Rr = pink (blend). Phenotype ratio 1
Important terms
- INCOMPLETE
- Neither allele hides fully.
- INCOMPLETE DOMINANCE AND CODOMINANCE
- Incomplete: heterozygote is in-between (red x white snapdragon -> pink school).
Overview
Study this learning unit in three steps:
Key Idea
Neither allele hides fully. 1 : 2 : 1 of three phenotypes. Do not call pink a 'mix of paint' in a chemistry way; it is gene expression. Snapdragon: RR = red, rr = white, Rr = pink (blend). Phenotype ratio 1:2:1 matches genotype ratio — unlike complete dominance where heterozygote looks dominant.
Examples RR red · Rr pink · rr white
Exam Application
Worked: IA i x IB i. Gametes: IA or i, and IB or i. Boxes: IAIB, IAi, IBi, ii. Children: AB, A, B, O possible (1:1:1:1 school).
Examples RR red · Rr pink · rr white
WHAT — INCOMPLETE DOMINANCE AND CODOMINANCE — INCOMPLETE
Neither allele hides fully. 1 : 2 : 1 of three phenotypes. Do not call pink a 'mix of paint' in a chemistry way; it is gene expression. Snapdragon: RR = red, rr = white, Rr = pink (blend). Phenotype ratio 1:2:1 matches genotype ratio — unlike complete dominance where heterozygote looks dominant. This page separates the idea from the wider topic “INCOMPLETE DOMINANCE AND CODOMINANCE” so it can be revised and assessed on its own.
WHY — Why this topic matters
INCOMPLETE DOMINANCE AND CODOMINANCE — INCOMPLETE is an independent FBISE learning unit because students must connect its structures and processes with their biological functions and examples.
HOW — How it works
Neither allele hides fully. 1 : 2 : 1 of three phenotypes. Do not call pink a 'mix of paint' in a chemistry way; it is gene expression. Snapdragon: RR = red, rr = white, Rr = pink (blend). Phenotype ratio 1:2:1 matches genotype ratio — unlike complete dominance where heterozygote looks dominant. Examples: RR red; Rr pink; rr white. Exam use: Worked: IA i x IB i. Gametes: IA or i, and IB or i. Boxes: IAIB, IAi, IBi, ii. Children: AB, A, B, O possible (1:1:1:1 school).
Explanation
Neither allele hides fully. 1 : 2 : 1 of three phenotypes. Do not call pink a 'mix of paint' in a chemistry way; it is gene expression. Snapdragon: RR = red, rr = white, Rr = pink (blend). Phenotype ratio 1:2:1 matches genotype ratio — unlike complete dominance where heterozygote looks dominant. Examples: RR red; Rr pink; rr white. Exam use: Worked: IA i x IB i. Gametes: IA or i, and IB or i. Boxes: IAIB, IAi, IBi, ii. Children: AB, A, B, O possible (1:1:1:1 school).
In simple words
Federal Board Class 11 Biology learning unit. Easy wording; no provincial-board material added.
Key points
- three phenotypes
- AB, A, B, O
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Incomplete Dominance and Codominance — Incomplete
Sticky Notes · Quick Revision
Core idea
- Neither allele hides fully. 1 : 2 : 1 of three phenotypes. Do not call pink a 'mix of paint' in a chemistry way; it is gene expression. Snapdragon: RR = red, rr = white, Rr = pink (blend). Phenotype ratio 1:2:1 matches genotype ratio — unlike complete dominance where heterozygote looks dominant. This page separates the idea from the wider topic “INCOMPLETE DOMINANCE AND CODOMINANCE” so it can be revised and assessed on its own.
WHAT
- Neither allele hides fully.
WHY
- INCOMPLETE DOMINANCE AND CODOMINANCE — INCOMPLETE is an independent FBISE learning unit because students must connect its structures and processes with their biological functions and examples.
HOW
- Neither allele hides fully. 1 : 2 : 1 of three phenotypes. Do not call pink a 'mix of paint' in a chemistry way; it is gene expression. Snapdragon: RR = red, rr = white, Rr = pink (blend). Phenotype ratio 1:2:1 matches genotype ratio — unlike complete dominance where heterozygote looks dominant. Examples: RR red; Rr pink; rr white. Exam use: Worked: IA i x IB i. Gametes: IA or i, and IB or i. Boxes: IAIB, IAi, IBi, ii. Children: AB, A, B, O possible (1:1:1:1 school).
Common misconception
- Do not treat incomplete as the same as every other part of incomplete dominance and codominance; define this unit and use its own evidence, steps, or conditions.
FBISE exam check
- Define incomplete dominance and codominance — incomplete, explain how it works, and support the answer with one relevant example.
60-second revision
- Neither allele hides fully.
- RR red
- Exam link: three phenotypes.
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