What are examples of discontinuous variation in plants?

Discontinuous variation in plants can be seen in traits such as flower colour, seed shape, and leaf arrangement.

Discontinuous variation refers to the type of variation where individuals fall into a number of distinct classes or categories, and is caused by genes. In plants, this can be observed in several ways. One of the most common examples is flower colour. For instance, in pea plants, the flower colour can either be purple or white, with no intermediate colours. This is because the gene for flower colour in pea plants has two alleles, one for purple and one for white. The purple allele is dominant, so plants with at least one purple allele will have purple flowers, while only those with two white alleles will have white flowers.

Another example of discontinuous variation in plants is seed shape. In Mendel's classic genetics experiments, he observed that pea plants could either have round or wrinkled seeds. This trait is controlled by a single gene with two alleles, one for round seeds and one for wrinkled seeds. The allele for round seeds is dominant, so plants with at least one round allele will produce round seeds, while only those with two wrinkled alleles will produce wrinkled seeds.

Leaf arrangement is another trait that shows discontinuous variation. Some plants have alternate leaf arrangement, where there is one leaf per node along the stem, while others have opposite leaf arrangement, with two leaves per node. This trait is controlled by genes, and a plant will either have one type of leaf arrangement or the other, with no intermediates.

In all these examples, the traits are controlled by a small number of genes, and each gene has a limited number of alleles. This results in a limited number of possible phenotypes, with clear distinctions between them, which is characteristic of discontinuous variation.