Final answer:
In a mapping cross, it is necessary to use both homozygous dominant and homozygous recessive individuals. This setup facilitates the determination of gene locations on chromosomes and requires a test cross using a dominant expressing individual with unknown genotype and a homozygous recessive individual.
Step-by-step explanation:
In setting up a mapping cross, the parental genotypes should include both homozygous dominant and homozygous recessive individuals. A mapping cross is used to determine the location of genes on a chromosome. In genetic analysis, this is done by crossing an individual with an unknown genotype, typically expressing a dominant trait, with an individual that is homozygous recessive for the trait in question.
This technique is known as a test cross. The offspring phenotypes provide information on the parent's genotype, because any appearance of the recessive phenotype indicates that the unknown parent is heterozygous for the dominant trait.