Colored aleurone in the kernels of corn is due to the dominant allele \(R\). The recessive allele \(r,\) when homozygous, produces colorless aleurone. The plant color (not the kernel color) is controlled by another gene with two alleles, \(Y\) and \(y\). The dominant \(Y\) allele results in green color, whereas the homozygous presence of the recessive \(y\) allele causes the plant to appear yellow. In a testcross between a plant of unknown genotype and phenotype and a plant that is homozygous recessive for both traits, the following progeny were obtained: $$\begin{array}{lc} \text { colored, green } & 88 \\ \text { colored, yellow } & 12 \\ \text { colorless, green } & 8 \\ \text { colorless, yellow } & 92 \end{array}$$ Explain how these results were obtained by determining the exact genotype and phenotype of the unknown plant, including the precise arrangement of the alleles on the homologs.

Step by step solution

01

Understand the given information

First, let's summarize the given information: - Aleurone color: Dominant allele \(R\) produces colored aleurone, recessive allele \(r\) produces colorless aleurone when homozygous (rr). - Plant color: Dominant allele \(Y\) produces green color, recessive allele \(y\) produces yellow color when homozygous (yy). - Testcross progeny results: $$\begin{array}{lc} \text{colored, green} & 88 \\ \text{colored, yellow} & 12 \\ \text{colorless, green} & 8 \\ \text{colorless, yellow} & 92 \end{array}$$ We have to determine the genotype and phenotype of the unknown parent plant.

02

Understand the testcross concept and identify the homozygous recessive parent

In a testcross, one individual of unknown genotype is crossed with a homozygous recessive individual. This means the homozygous recessive parent has the genotype "rr yy."

03

Analyzing the progeny's phenotype ratios

Based on the given ratios of progeny phenotypes, let's analyze them and determine which alleles are likely to be present in the unknown parent: 1) \(\frac{88}{100}\) colored, green and \(\frac{12}{100}\) colored, yellow suggest that the unknown parent has the dominant color allele R. 2) Similarly, the ratio of green to yellow progeny, \(\frac{88+8}{100}\) green and \(\frac{12+92}{100}\) yellow, suggests that the unknown parent has a heterozygous genotype for the plant color, meaning they have one dominant Y allele and one recessive y allele.

04

Determine the exact genotype and phenotype of the unknown parent

Combining the results of steps 3 and 4, we can now determine the unknown parent's genotype and phenotype. Genotype: R_ Yy (where _ indicates either R or r, as we don't have enough information to identify the second allele in the R locus.) Phenotype: colored aleurone and green plant color

05

Explain the progeny results based on the determined genotype

Since we determined that the unknown parent's genotype is R_ Yy, we can now explain the results obtained in the testcross progeny. 1) The R_ Yy parent crossed with the rr yy parent could produce the following genotypes: - Rr Yy (colored, green): gives the highest probability of occurrence, 88 out of 100 progeny. - Rr yy (colored, yellow): least probability of occurrence, 12 out of 100 progeny. - rr Yy (colorless, green): least probability of occurrence, 8 out of 100 progeny. - rr yy (colorless, yellow): gives the highest probability of occurrence, 92 out of 100 progeny. This matches the observed progeny results. 2) The arrangement of alleles on homologs can be depicted as: Unknown parent: RY / Ry Homozygous recessive parent: ry / ry Considering these alleles and the progeny results, we can conclude that the unknown parent's genotype is R_ Yy and its phenotype is colored aleurone and green plant color.

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