Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category: Education
Input types: number, select
Output type: json
Sample coverage: 4
API ready: Yes

Overview

Test Cross Analyzer determines whether a dominant-phenotype parent is likely homozygous (AA) or heterozygous (Aa) from offspring counts in a cross with aa, using a selected significance level and decimal precision.

When to use

Determine whether a dominant-phenotype organism is AA or Aa using test-cross offspring data.
Confirm heterozygosity when at least one recessive-phenotype offspring is observed.
Evaluate how strongly zero recessive offspring support a likely homozygous result.

How it works

1Enter the numbers of dominant- and recessive-phenotype offspring.
2The analyzer treats any recessive offspring as evidence that the tested parent is heterozygous (Aa).
3When no recessive offspring are observed, it calculates P(0 recessive) = 0.5^n under the heterozygous hypothesis and compares it with the selected significance level.
4The JSON result reports the total offspring, observed ratio, conclusion, genotype, and relevant probability or confidence values.

Use cases

Teaching Mendelian genetics and test-cross logic in biology classes.
Checking genotype-determination exercises with observed dominant and recessive offspring counts.
Exploring how sample size changes confidence in a likely homozygous conclusion.

Examples

1. Recessive offspring confirm heterozygosity

Biology student

Background

A student performs a test cross and records 47 dominant-phenotype and 53 recessive-phenotype offspring.

Problem

Determine whether the parent with the dominant phenotype is AA or Aa.

How to use

Enter dominantCount as 47, recessiveCount as 53, select alpha 0.05, and use 4 decimal places.

{"dominantCount":47,"recessiveCount":53,"alpha":"0.05","decimalPlaces":4}

Outcome

The result identifies the parent as heterozygous (Aa). The observed 47:53 ratio is close to the expected 1:1 ratio for Aa × aa.

2. Zero recessive offspring support a likely homozygous result

Genetics instructor

Background

An instructor reviews a test cross with 20 dominant-phenotype offspring and no recessive-phenotype offspring.

Problem

Assess whether the absence of recessive offspring is unlikely under the heterozygous hypothesis.

How to use

Enter dominantCount as 20, recessiveCount as 0, select alpha 0.05, and use 4 decimal places.

FAQ

What cross does this analyzer assume?

It assumes a test cross between a dominant-phenotype parent with an unknown genotype and a recessive homozygote, aa.

What does a recessive offspring prove?

A recessive offspring shows that the tested parent contributed a recessive allele, so the parent is heterozygous (Aa).

What does zero recessive offspring mean?

Zero recessive offspring suggests the parent is likely homozygous (AA), with strength depending on the total offspring count and selected significance level.

Which significance levels are available?

You can select 0.05, 0.01, or 0.001.

Is this tool intended for clinical or production decisions?

No. The analyzer is intended for educational use only.

{"dominantCount":20,"recessiveCount":0,"alpha":"0.05","decimalPlaces":4}

Test Cross Analyzer (determine homozygous vs heterozygous)

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Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Overview

When to use

How it works

Use cases

Examples

1. Recessive offspring confirm heterozygosity

2. Zero recessive offspring support a likely homozygous result

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