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Biology
Posted 7 months ago

In a certain plant, tall, T\mathrm{T} is dominant to short, t\mathrm{t}. Red flowers, R\mathrm{R} is dominate to white flowers, r\mathrm{r}. A gardener crosses a TtRr plant with a ttrr plant. Seeds from this cross produced 52 plants which are tall and red and 48 plants that are short and white. Explain these results.
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Answer from Sia
Posted 7 months ago
Answer
The results can be explained by the Mendelian principles of inheritance, where the TtRr plant can produce gametes with TR, Tr, tR, and tr alleles, and the ttrr plant can only produce gametes with tr alleles. The offspring genotypes and phenotypes are a result of the combination of these gametes.
Solution
a
Parental Genotypes: The TtRr plant can produce four types of gametes (TR, Tr, tR, tr), while the ttrr plant can only produce one type of gamete (tr)
b
Offspring Genotypes: The possible genotypes of the offspring are TtRr, Ttrr, ttRr, and ttrr
c
Offspring Phenotypes: The TtRr and Ttrr genotypes will result in tall and red plants, while the ttRr genotype will result in short and red plants, and the ttrr genotype will result in short and white plants
d
Phenotypic Ratio: Since the ttrr plant can only pass on the tr alleles, all offspring will be heterozygous for at least one trait. The observed phenotypic ratio is approximately 1:1 for tall and red to short and white, which is not the expected 1:1:1:1 ratio for a dihybrid cross. This suggests that some offspring with the ttRr genotype may have been misclassified or unaccounted for
Key Concept
Mendelian inheritance and the law of segregation explain the genotypic and phenotypic ratios in the offspring of a dihybrid cross.
Explanation
The observed phenotypic ratio of tall and red to short and white plants (approximately 1:1) can be explained by the Mendelian inheritance patterns, where each parent contributes one allele for each trait to their offspring. The deviation from the expected 1:1:1:1 ratio suggests a possible error in classification or observation of the offspring.

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