Define test cross.

Explanation

**Step-by-Step Text Solution:**

1. **Definition of Test Cross**: A test cross is a genetic cross performed to determine the genotype of an individual that exhibits a dominant phenotype but has an unknown genotype.

2. **Purpose of Test Cross**: The main purpose of a test cross is to ascertain whether the dominant phenotype individual is homozygous dominant (having two identical alleles) or heterozygous (having one dominant and one recessive allele).

3. **Method of Test Cross**: The individual with the dominant phenotype is crossed with a homozygous recessive individual. The recessive individual has a known genotype, which is represented by two recessive alleles (e.g., "tt" for a trait where "T" is dominant).

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