Question

in the boxes above each pea plant with the alleles found in that pea
p₁
short pea plant tall pea plant
f₁

Explanation:

Step1: Identify parental genotypes

Short pea plants are homozygous recessive, so genotype is $tt$. Tall pea plants in true-breeding P₁ generation are homozygous dominant, so genotype is $TT$.

Step2: Determine F₁ genotypes

Each parent passes one allele: $t$ from short, $T$ from tall. All F₁ offspring get $Tt$.

Answer:

P₁ Short pea plant box: $tt$
P₁ Tall pea plant box: $TT$
F₁ box: $Tt$