Epistasis Ratio Calculator (modified dihybrid ratios)
Compute modified F2 phenotypic ratios from two-locus gene interaction: 9:7, 9:3:4, 12:3:1, 13:3, 15:1, 9:6:1 or 9:3:3:1, with expected counts and optional chi-square goodness-of-fit. Derived from Mendel 1866, Bateson & Punnett 1905, Griffiths, Hartl & Clark 2007. Educational use only.
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Tool usage guide
Learn when to use this tool, what it supports, and how real users apply it.
Key facts
Category
Education
Input types
select, number, text
Output type
json
Sample coverage
4
API ready
Yes
Overview
The Epistasis Ratio Calculator computes expected F2 phenotypic ratios and counts for an AaBb × AaBb cross under independent assortment or six common two-locus interaction models: 9:7, 9:3:4, 12:3:1, 13:3, 15:1, and 9:6:1. Enter optional observed phenotype counts to perform a chi-square goodness-of-fit test. Educational use only.
When to use
Calculate expected phenotype counts from a selected modified dihybrid ratio and total F2 offspring.
Compare observed phenotype counts with an independent 9:3:3:1 expectation or an epistasis ratio.
Review whether observed counts show a significant chi-square deviation from the selected theoretical ratio.
How it works
1Select the interaction type, such as complementary genes, recessive epistasis, or no interaction.
2Enter the total number of F2 offspring to convert ratio parts into expected phenotype counts.
3Optionally enter comma-separated observed counts in the same order as the phenotype classes.
4The calculator returns JSON with the ratio, phenotype classes, expected counts, and optional chi-square goodness-of-fit results.
Use cases
Teaching how two-locus gene interactions modify the classic Mendelian dihybrid ratio.
Estimating phenotype counts for classroom genetics exercises and F2 cross planning.
Testing example breeding data against a proposed epistasis model with chi-square goodness of fit.
Examples
1. Calculate a 9:7 complementary-gene expectation
Genetics student
Background
A student is studying complementary gene action in sweet peas and wants expected flower-color counts for 160 F2 offspring.
Problem
Convert the 9:7 ratio into expected colored and white phenotype counts.
How to use
Select Complementary genes (9:7), enter 160 for Total F2 offspring, and leave observed counts blank.
The calculator returns 90 colored offspring and 70 white offspring, corresponding to 56.25% and 43.75% of the F2 total.
2. Test Mendelian dihybrid data against 9:3:3:1
Biology instructor
Background
An instructor uses Mendel's seed shape and color counts: 315 round yellow, 108 wrinkled yellow, 101 round green, and 32 wrinkled green, for a total of 556.
Problem
Determine whether the observed counts fit the no-interaction 9:3:3:1 expectation.
How to use
Select No interaction (9:3:3:1), enter 556 as the total, and enter observed counts as 315, 108, 101, 32.
FAQ
What cross does the calculator use?
It models an AaBb × AaBb F2 cross with two loci.
Which ratios are supported?
It supports 9:3:3:1, 9:7, 9:3:4, 12:3:1, 13:3, 15:1, and 9:6:1.
What should I enter for total F2 offspring?
Enter the total number of F2 individuals used to calculate expected counts.
How do I enter observed counts?
Enter comma-separated counts, one for each phenotype class, following the listed class order.
Is the calculator intended for clinical or research decisions?
Expected counts are 312.75, 104.25, 104.25, and 34.75. The chi-square result is 0.47 with 3 degrees of freedom and is not significant at α = 0.05.
3. Compare observed counts with recessive epistasis
Genetics learner
Background
A learner has phenotype counts from an AaBb × AaBb exercise and wants to evaluate a recessive-epistasis model.
Problem
Use the 9:3:4 model to calculate expected counts and compare them with the observed class totals.
How to use
Select Recessive epistasis (9:3:4), enter the total F2 offspring, and provide three observed counts in the phenotype-class order shown by the calculator.
Outcome
The calculator returns the 9:3:4 expected distribution and, when observed counts are supplied, provides the corresponding chi-square goodness-of-fit result.