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?
3 red-flowered plants: 1 white-flowered plant
In a monohybrid cross of Rr x Rr, the expected phenotypic ratio is derived from the potential combinations of alleles in the offspring. The dominant red flower color (R) will express itself in 75% of the offspring, while the recessive white flower color (r) will appear in 25%, leading to a classic 3:1 ratio.
This choice accurately reflects the expected phenotypic ratio from the cross Rr x Rr. The possible allele combinations are RR, Rr, Rr, and rr, resulting in three representations of red flowers (RR and Rr) and one representation of white flowers (rr).
This choice is incorrect because it reverses the expected ratio. In the Rr x Rr cross, the recessive white flower phenotype only appears in the homozygous recessive genotype (rr), which accounts for 25% of the offspring, not 75%.
This choice is fundamentally incorrect as it suggests that all offspring would show the recessive phenotype. Given the presence of the dominant allele R in both parents, a portion of the offspring will inherit the dominant trait, resulting in red flowers.
This option is also incorrect because it implies that every offspring will display the dominant phenotype. However, the presence of the homozygous recessive genotype (rr) in 25% of the offspring means that not all will be red-flowered; some will indeed be white-flowered.
The inheritance of flower color in this plant species follows classic Mendelian principles, resulting in a phenotypic ratio of 3 red-flowered plants for every 1 white-flowered plant from the cross Rr x Rr. The dominant allele R overshadows the recessive allele r, creating a predictable pattern in the offspring's appearance. Understanding these ratios not only illustrates basic genetic principles but also aids in predicting traits in breeding programs.
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