Practice question

Wide hybridization with chromosome elimination exploits post-zygotic incompatibility where chromosomes of one parent are selectively lost during early embryonic divisions due to centromere incompatibility. In cereal DH production, wheat Triticum aestivum crossed as female to maize Zea mays as pollinator leads to fertilization but maize chromosomes fail to attach to wheat spindle due to centromere divergence and asynchronous mitosis, becoming micronuclei and eliminated within few divisions. Resulting embryo contains only haploid wheat chromosomes, rescued via embryo culture on artificial medium before endosperm abortion because endosperm also degenerates. Similarly barley × Hordeum bulbosum system uses bulbosum elimination to produce barley haploids. This method achieves broad genotype independence, avoids albinism problem common in anther culture of cereals, and produces stable haploids that are doubled with colchicine into fertile DH. In wheat breeding it is standard for DH population development for mapping and variety extraction, producing hundreds of homozygous lines per year efficiently. Embryo rescue media typically contain high sucrose, auxins, and cytokinins to support weak haploid embryos that lack functional endosperm; after rescue, haploid seedlings verified by morphological markers like reduced vigor and sterility, then treated with colchicine to double chromosomes and restore fertility for selfing and seed multiplication.