In a cross, an individual with an unknown genotype is mated with an individual with a homozygous recessive genotype to determine the unknown genotype.

This process is known as a test cross. Here are the steps:

1. Identify the Phenotypes: The first step is to identify the physical characteristics or phenotypes of the two individuals. The individual with the unknown genotype will display the dominant trait, while the individual with the homozygous recessive genotype will display the recessive trait.

2. Set Up the Punnett Square: A Punnett square is a diagram used to predict the outcome of a particular cross or breeding experiment. It is named after Reginald C. Punnett, who devised the approach. The Punnett square is a square divided into four parts. The alleles of the individual with the unknown genotype are written on the top of the square, while the alleles of the individual with the homozygous recessive genotype are written on the side of the square.

3. Fill in the Punnett Square: Each box within the square is filled by combining one allele from the top of the square with one allele from the side of the square.

4. Analyze the Results: The genotype of the offspring can be determined by analyzing the results in the Punnett square. If any of the offspring display the recessive trait, then the individual with the unknown genotype must be heterozygous. If all of the offspring display the dominant trait, then the individual with the unknown genotype is likely homozygous dominant.