Final answer:
In a dihybrid cross of TtYy x ttyy, the phenotypic ratios in the offspring are 1:1:1:1, each representing combinations of dominant and recessive traits of the parents.
Step-by-step explanation:
In a dihybrid cross involving parents with genotypes TtYy and ttyy, we need to consider both traits (T or t, and Y or y) independently to determine the phenotypic ratios in the offspring. Each trait follows a Mendelian inheritance pattern where T and Y are dominant alleles, and t and y are recessive alleles. The first parent (TtYy) can produce gametes with the following combinations: TY, Ty, tY, and ty. The second parent (ttyy) can only produce gametes with the combination ty.
To predict the phenotypic ratios, we create a Punnett square for this dihybrid cross. Since the second parent is homozygous recessive for both traits (t and y), all offspring will inherit a t and y from this parent. Consequently, the phenotypic ratio only depends on the alleles contributed by the first parent (TtYy). The potential offspring phenotypes will be as follows: TtYy (which exhibits the dominant T and Y phenotypes), Ttyy (which exhibits the dominant T phenotype and the recessive y phenotype), ttYy (which exhibits the recessive t phenotype and the dominant Y phenotype), and ttyy (which exhibits both recessive t and y phenotypes).
The phenotypic ratio will therefore be 1:1:1:1 corresponding to each of these phenotypes respectively.