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In a red and white-flowered cross of Mir...

In a red and white-flowered cross of Mirabilis jalapa, F, generation has red, pink and white-flowered plants in the ratio of

A

` 2:1:1`

B

` 1:1:2`

C

`1:2:1`

D

`1:0:1`

Text Solution

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The correct Answer is:
To determine the flower color ratio in the F2 generation of a cross between red and white-flowered Mirabilis jalapa, we can follow these steps: ### Step-by-Step Solution: 1. **Identify the Parental Generation**: - The parental plants are red-flowered (RR) and white-flowered (rr). - Here, "R" represents the allele for red flowers, and "r" represents the allele for white flowers. 2. **Determine the F1 Generation**: - When the red-flowered plant (RR) is crossed with the white-flowered plant (rr), all offspring in the F1 generation will be heterozygous (Rr). - Since R is dominant over r, all F1 plants will exhibit the red flower phenotype. 3. **Self-Fertilization of F1 Generation**: - When the F1 generation (Rr) is self-fertilized, we need to set up a Punnett square to determine the genotypes of the F2 generation. 4. **Create a Punnett Square**: - The gametes from the F1 generation (Rr) can produce two types of gametes: R and r. - Set up the Punnett square: ``` R | r --------------- R | RR | Rr --------------- r | Rr | rr ``` 5. **Analyze the Results**: - From the Punnett square, we can see the following genotypes: - 1 RR (homozygous red) - 2 Rr (heterozygous red) - 1 rr (homozygous white) - This gives us a total ratio of 1:2:1 for the genotypes. 6. **Determine the Phenotypic Ratio**: - Since both RR and Rr produce red flowers, the phenotypic ratio in the F2 generation will be: - 3 red-flowered plants (1 RR + 2 Rr) - 1 white-flowered plant (1 rr) - Thus, the phenotypic ratio is 3 red: 1 white. 7. **Conclusion**: - The final ratio of flower colors in the F2 generation of Mirabilis jalapa is 3 red: 1 white. However, since pink flowers are also present due to incomplete dominance, the overall ratio of red, pink, and white flowers is 1:2:1. ### Final Answer: The F2 generation of Mirabilis jalapa has red, pink, and white flowers in the ratio of 1:2:1. ---
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