Flower color is controlled by a single pair of alleles. The allele for red flowers is dominant to the allele for white flowers. A plant homozygous for red flowers is crossed with a plant homozygous for white flowers. All the resulting plants have red flowers (F1 generation). When the F1 generation crosses with each other, 18 plants are obtained. 12 plants have red flowers and 6 have white flowers (F2 generation). What ratio is expected in the F2 generation and what ratio has been obtained?
Correct answer: A. 3:1 expected, 2:1 obtained
- A. 3:1 expected, 2:1 obtained
- B. 2:1 expected, 3:1 obtained
- C. 1:1 expected, 3:1 obtained
- D. 1:1 expected, 2:1 obtained
Explanation
The correct answer is that the expected ratio in the F2 generation is 3:1, and the obtained ratio is 2:1. In a typical Mendelian monohybrid cross (Rr x Rr), the expected phenotypic ratio is 3:1, with three plants having the dominant phenotype (red flowers) for every one plant with the recessive phenotype (white flowers). The obtained ratio of 2:1 suggests a deviation from the expected, possibly due to a small sample size or experimental error. The other options incorrectly present the expected and obtained ratios.
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About Inheritance
Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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