5005 Praxis Practice Test Practice Question
In a species of flowering plant, red flower color is dominant to white flower color, where R is the dominant allele and r is the recessive allele. What is the expected phenotypic ratio of the offspring from the cross Rr * Rr?
Correct Answer: A
Rationale: The expected phenotypic ratio from the cross Rr x Rr is derived from a Punnett square. This cross produces offspring with genotypes RR, Rr, Rr, and rr. The dominant allele R results in red flowers, while the recessive allele r results in white flowers. Thus, the genotypes RR and Rr (three out of four) yield red flowers, while only rr (one out of four) results in white flowers, leading to a ratio of 3 red-flowered plants to 1 white-flowered plant.
Option B is incorrect as it reverses the ratio. Option C suggests all offspring are white, which is impossible given the presence of dominant alleles. Option D claims all offspring are red, overlooking the possibility of the recessive genotype.
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