For ASLAN pls. Expalin what David feels when he is working in the fields? Why might this be ironic?

Hey, David is working in the fields when he feels this high frequency telepathic signal come crashing through his brain. It's actually from Petra, his little sister. I suppose the irony is that both of his father's kids are mutants. This means that Joseph has mutant DNA ; in a sense he is what he most reviles.