You are given 1 plant bearing red flowers, and 1 plant bearing yellow flowers. Y

Question

You are given 1 plant bearing red flowers, and 1 plant bearing yellow
flowers. You are not told anything else about the plants, and you do not have any other
plants of this species to work with.
A. You perform a number of crosses between the red and yellow plant, resulting in 23
red plants and 25 yellow plants. What are two different ways that this result could be
interpreted? Give the genotypes of the Fo plants in the case of each interpretation.

B. Describe an experiment (a specific cross) that would allow you to determine which of the above interpretations is true. For each possible experimental outcome, describe the conclusion that you would draw from your results

Explanation / Answer

A. The alleles of this gene correspond to only one trait and so we use a monohybrid cross. We can choose one allele to be dominant and the other to be recessive. a) First let's assume the dominant allele for color (red) is R and that the recessive allele for color (yellow) is r. Since the F1 plants have a nearly 1:1 (red:yellow) phenotypic ratio, and since we know that parents (F0) were red and yellow, the genotypes must be heterozygote for the dominant allele: Rr (red) and homozygous for the recessive allele: rr (yellow). The Punnett square analysis for these genotypes will yield the observed 1:1 ratio. b) A similar argument can be made using Y as the dominant allele for color (yellow) and y as the recessive allele for color (red). F0 genotypes are Yy (yellow) and yy (red). B. To test the interpretation in a), we self-cross heterozygote F1 plants (Rr). This should give us a 1:2:1 genotypic ratio (AA:Aa:aa) and 3:1 phenotypic ratio (red:yellow) in the F2 generation. Since these ratios arise, it must mean that the red phenotype must be dominant to the yellow phenotype. A similar experiment can be done to test the interpretation in b).

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