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Test Cross Ratio Calculator

Work out test cross ratio instantly with clear inputs, formula shown and shareable results.

About Test Cross Ratio Calculator

Compares observed recessive offspring from a cross to a homozygous recessive tester with the expectation under each hypothesis for the unknown parent.

Formula

Test cross

Crossing with aa gives 50% recessive offspring if the unknown parent is Aa and none if it is AA

Worked example

With the default values below, Test Cross Ratio Calculator returns Recessive offspring expected of 50.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Hypothesis for the unknown parentone of Homozygous dominant AA, Heterozygous Aa
Heterozygous Aa
Offspring producedaccepts 1–100,000
100
Recessive offspring observedaccepts 0–100,000
46

Results

Recessive offspring expected
50.00
Observed recessive share
46.00%
Expected recessive share
50.0%
Inference
Consistent with a heterozygous parent if about half the offspring are recessive

Step by step

  1. 1Values used
  2. 2Test cross
  3. 3Recessive offspring expected= 50.00
  4. 4Observed recessive share= 46.00
  5. 5Expected recessive share= 50.0
  6. 6Inference= Consistent with a heterozygous parent if about half the offspring are recessive

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How many offspring are needed?

Ten offspring with no recessives gives about a 0.1% chance of missing a heterozygous parent, so around ten is usually enough.

Does one recessive offspring settle it?

Yes. A single recessive offspring proves the unknown parent carries the recessive allele.

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