Final answer:
The purple stem trait variation is an example of simple dominance, as the dominant trait (purple color) is expressed in both homozygous dominant and heterozygous plants. This contrasts with the possibly more complex inheritance of the tongue-rolling trait in humans. Mendelian genetics, with its predictable ratios of offspring traits, can help in understanding these trait variations.
Step-by-step explanation:
The purple stem trait variation and the tongue-rolling trait variation are different in how they are inherited and expressed. In simple dominance, as seen with the purple stem trait in plants, the trait is visible whenever the dominant allele is present in either a homozygous (BB) or heterozygous (Bb) state. Therefore, if a plant is purple, it can be either BB or Bb, but if it has two recessive alleles (bb), the plant will have white flowers. This is different from the tongue-rolling trait in humans, which may have a more complex genetic basis or may not follow simple dominance as closely as flower color in pea plants.
Given the provided information, the color purple is the dominant trait in pea plants, and the likelihood of these traits appearing in offspring can be predicted using Mendelian genetics. For example, in Gregor Mendel's classic pea plant experiments, he discovered that certain traits, such as flower color and seed shape, followed specific inheritance patterns. When a purple-flowered plant (dominant trait) was crossed with a white-flowered plant (recessive trait), all the F1 generation exhibited the purple-flowered trait. However, when F1 plants were cross-pollinated, the F2 generation showed a mix of both purple and white flowers, in a 3:1 ratio, indicating that the white-flowered plants were homozygous recessive, and purple-flowered plants could be either homozygous dominant or heterozygous.
Similarly, in genetic experiments with fruit flies, certain traits are inherited following Mendelian genetics and can be predicted through crosses. For example, a true-breeding wild-type fly with a true-breeding fly with a mutant phenotype results in all F1 progeny displaying the wild-type phenotype, indicating the dominance of the wild-type traits.