Figure 2

Model of coevolution of B attack and A defence in a native maize population. At meiosis B loss is prevented in homozygous fBth fBth plants. The A defence is provided by the fBtl dominant allele. At fertilisation, B attack occurs in mBth egg cells which are preferentially fertilised by B carrying male gametes. Egg cells with the mBtl allele tend to counteract B accumulation, because they are fertilised by 0B or 2B sperm nuclei at random.