Practice question

In a backcross program two parents play distinct roles. Donor parent, also called non-recurrent parent, carries elite allele missing in adapted cultivar but is otherwise agronomically inferior. Recurrent parent is the high-yielding, widely adapted cultivar targeted for improvement, used as female or male in every backcross to restore its genome. After initial F1 = donor × recurrent, selected progeny possessing donor allele is crossed again to same recurrent parent, producing BC1F1, then BC2F1, and so on. Repeated use elevates proportion of recurrent genome from 75% in BC1 to 87.5% in BC2, 93.75% in BC3, following 1-(1/2)^(n+1). Recurrent parent is thus recipient background that must be recovered fully, while donor segment around target locus shrinks through recombination. Choice of recurrent parent determines final cultivar adaptation, so elite lines with broad stability and market acceptance are preferred to maximize commercial impact of introgression. Cytoplasmic background usually comes from recurrent parent when used as female in final backcross, ensuring nuclear-cytoplasmic compatibility and preserving cytoplasmic male sterility systems or organelle encoded traits important for hybrid seed production.