The tall-stem and short-stem alleles in pea plants are different forms of the same gene. Here's why:

* Genes: Genes are segments of DNA that code for specific traits. In this case, the gene in question determines stem length in pea plants.

* Alleles: Alleles are alternative forms of a gene. So, the tall-stem allele and the short-stem allele are both versions of the same gene, but they have different DNA sequences that lead to different expressions of the trait (stem length).

It's like having two different versions of a recipe for a cake, both using the same basic ingredients but yielding different results (one tall and fluffy, the other short and dense).

This concept is fundamental to understanding inheritance patterns and how traits are passed down through generations.