The production of gametes by the parents, formation of zygotes, the F₁ and F₂ plants, can be understood from a diagram called :

The correct answer is Punnett square.

A Punnett square is a diagram that visually represents the combination of alleles from the gametes of two parent organisms. By listing the possible gametes of each parent along the top and side of a grid, the square shows all potential genotype combinations for the offspring.

When the parents produce gametes, each gamete carries one allele for each gene. The Punnett square pairs each gamete from one parent with each gamete from the other parent, effectively illustrating the formation of zygotes (the fertilized eggs). This grid therefore predicts the genotypic ratios among the first filial generation ($F$₁).

By treating the $F$₁ individuals as new “parents” and repeating the process—drawing a new Punnett square for their gametes—we can predict the genotypic distribution in the second filial generation ($F$₂). Hence, the Punnett square diagram neatly captures the production of gametes, formation of zygotes, and the genetic outcomes for both $F$₁ and $F$₂ plants.

Therefore, among the given options, the diagram that best fits this description is the Punnett square.