A geneticist investigates the inheritance of two characteristics in tomato plants: stem colour (controlled by gene $A/a$) and leaf shape (controlled by gene $B/b$).

A homozygous dominant plant ($AABB$) is crossed with a homozygous recessive plant ($aabb$) to produce heterozygous $F_1$ offspring ($AaBb$).

To determine the degree of linkage between these two genes, an $F_1$ plant is backcrossed with a double homozygous recessive plant ($aabb$). The resulting phenotypes and numbers of the $F_2$ offspring are shown below:

• Dominant stem colour, dominant leaf shape: 364
• Recessive stem colour, recessive leaf shape: 356
• Dominant stem colour, recessive leaf shape: 142
• Recessive stem colour, dominant leaf shape: 138

The diagram below illustrates how crossing over (chiasma formation) between linked loci during meiosis generates these recombinant chromatids:

Based on these results, what is the recombination frequency between gene $A$ and gene $B$?