Codominance Calculator

Codominant 2×2 Grid

	CR	CW
CR	CRCR	CRCW
CW	CRCW	CWCW

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Trait Probabilities

Genotype Ratio

Phenotype Ratio (Both Expressed)

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Expert Tip

In codominance, the heterozygous genotype has a unique phenotype representing co-expression (e.g. Roan has both red and white hairs), rather than a mixture or blending of the two.

Methodology & Equations

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Roan Horse/Cattle Codominance

Under codominance inheritance model:

- **C<sup>RCR:** Red coat phenotype.
- **CRCW:** Roan coat phenotype (co-expression of both red and white patches).
- **CWCW:** White coat phenotype.</sup>

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Heterozygous Crosses

Crossing two roan individuals (C<sup>RCW × CRCW) results in:

- 25% Red (CRCR)
- 50% Roan (CRCW)
- 25% White (CWCW)

Here, the phenotypic ratio matches the genotypic ratio exactly (1:2:1).</sup>

How to Predict Codominant Inheritance: Step-by-Step

Below is a step-by-step example crossing a red parent (C^{RCR) with a roan parent (CRCW):}

1

Determine Parent Alleles

Parent 1 (C^{RCR) can only pass on the CR allele. Parent 2 (CRCW) can pass on either CR or CW.}

2

Fill the 2x2 Punnett Square

Place Parent 1 alleles (C^{R, CR) on top, and Parent 2 alleles (CR, CW) on the left side:
Top Row Cells: CRCR, CRCR.
Bottom Row Cells: CRCW, CRCW.}

3

Determine Phenotypes

Analyze the offspring genotypes:
- 50% C<sup>RCR translates to 50% Red coat.
- 50% CRCW translates to 50% Roan coat (co-expressed red and white hair patches).</sup>

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