Two pure lines of four-o'clock plants, one with red flowers and the other with white flowers, are crossed. The F1 progeny all are pink. When these are selfed, the F2 progeny are 25 percent red flowers, 50 percent pink flowers, and 25 percent white flowers. This is an example of____________.

Answer: This is an example of incomplete dominance. Incomplete dominance is a form of inheritance wherein the offspring's phenotype is a blend or mixture of the parents' phenotypes.

In this specific case with the four-o'clock plants, the red-flowered plant and the white-flowered plant are pure lines, meaning they are homozygous for their respective flower color genes. When they are crossed, the F1 generation inherits one allele for red and one allele for white, but instead of one completely dominating the other, they blend and result in pink flowers—a color intermediate between red and white.

When these F1 progeny are self-pollinated, they produce F2 offspring with the following ratios: 25 percent red (RR), 50 percent pink (RW), and 25 percent white (WW). This ratio fits a 1:2:1 pattern that is expected when an organism with a heterozygous pair of alleles (RW) is self-fertilized.

In terms of genetics, the alleles for flower color would be represented as R for red and W for white. The F1 plants are all RW, and so the mating of F1 plants (RW x RW) will produce the following genotypes in the F2 generation: - RR (red, homozygous), - RW (pink, heterozygous), - WR (pink, heterozygous, but the same as RW due to allele symmetry), and - WW (white, homozygous).

This results in a phenotypic ratio of 1 red : 2 pink : 1 white (RR : RW/WR : WW).