The given question is incorrect. The correct question is:
Question: In a dihybrid cross, the F2 will have nine genotypes, but only four phenotypes because the ........ genes cause the ......traits to mask the ..... traits.
Answer:
In a dihybrid cross, the F2 will have nine genotypes, but only four phenotypes because the HETEROZYGOUS genes cause the DOMINANT traits to mask the RECESSIVE traits.
Step-by-step explanation:
In a dihybrid cross, only four phenotypic classes are observed while there is a total of nine different genotypes. This occurs since many F2 genotypes are heterozygous for one or another gene. These heterozygous genotypes produce only dominant trait while the recessive traits are masked. For example, a dihybrid cross TtRr x TtRr gives nine different genotypes. The genotype TtRR, TtRr, TTRR, and TTRr would express the dominant traits for both the genes and would have the same phenotype.