Final answer:
A plant with magenta petals exhibits incomplete dominance, resulting in a phenotype that blends the red and white homozygous conditions. Therefore, it must have one dominant allele for the red color and one recessive allele for the white color, represented as Rw.
Step-by-step explanation:
To determine which alleles a plant with magenta petals might have for two genes, we need to understand the concepts of dominance and co-dominance in genetics. In the scenario described, there is a display of incomplete dominance, where the heterozygous condition results in a phenotype that is a blend of the two homozygous phenotypes—specifically, magenta petals as the result of a cross between plants with red and white petals.
Since magenta is not described as the result of either homozygous condition (red or white), but a blend, we can deduce that the alleles for magenta petals would reflect a heterozygous condition. This means one allele for the red color and one allele for the white color. Conventional genetic abbreviation establishes that the dominant allele is capitalized and the recessive allele is lowercase.
Given that no dominant allele for magenta is described, and the plant does not express the pure red or white phenotype, the correct genetic make-up for magenta petals would be one red allele and one white allele. Therefore, we can conclude that a plant with magenta petals must have a dominant allele for gene 1 and a recessive allele for gene 2. In standard genetic notation, this could be represented as Rw if we assume 'R' is the dominant allele for red color and 'w' is the recessive allele for white color, leading to a magenta, or pink, phenotype when they are together.