Final answer:
In a test-cross, if half of the offspring have the phenotype "A" and half have the phenotype "a", it means that one parent is heterozygous (Aa) and the other parent is homozygous recessive (aa).
Step-by-step explanation:
In the given question, we are told that Individual #1 with phenotype "A" is test-crossed and half of the offspring produced have phenotype "A" and half have a phenotype "a". From this information, we can determine the genotypes of the individuals that were crossed.
In this case, since half of the offspring have the phenotype "A", it means that Individual #1 must be heterozygous (Aa) because the dominant trait is expressed. The other parent in the cross must be homozygous recessive (aa) in order to produce offspring with the phenotype "a". Therefore, the genotypes of the individuals that were crossed are Aa and aa.