To determine which genotypes Mendel could have used to represent the cross for flower color, let's analyze the given options step-by-step.
The term "heterozygous" refers to having two different alleles for a particular gene. In this context of flower color, a heterozygous genotype would consist of one dominant and one recessive allele.
Let's break down each option:
1. [tex]$PP \times PP$[/tex]
- [tex]$PP$[/tex] represents a homozygous dominant genotype.
- Both plants have two copies of the dominant allele.
- This does not involve any heterozygous individuals.
2. [tex]$P p \times P p$[/tex]
- [tex]$Pp$[/tex] represents a heterozygous genotype, with one dominant allele (P) and one recessive allele (p).
- Both plants are heterozygous for the trait of flower color.
- This matches the description of crossing heterozygous plants.
3. [tex]$pp \times pp$[/tex]
- [tex]$pp$[/tex] represents a homozygous recessive genotype.
- Both plants have two copies of the recessive allele.
- This does not involve any heterozygous individuals.
4. [tex]$P p \times P P$[/tex]
- One plant is heterozygous ([tex]$Pp$[/tex]), and the other plant is homozygous dominant ([tex]$PP$[/tex]).
- This involves one heterozygous individual, but not both.
- This does not fully match the description of crossing two heterozygous plants.
Given these evaluations, the correct option that addresses Mendel crossing two plants that are both heterozygous for the trait of flower color (having the 'Pp' genotype) is:
- [tex]$P p \times P p$[/tex]
So, the answer is [tex]$P p \times P p$[/tex].
