Practice question

Conventional pedigree inbreeding reduces heterozygosity by half each selfing generation, requiring F6-F7 to attain >98% homozygosity, a process taking 5-6 years. Doubled haploid approach collapses this timeline to single step through manipulation of gametic pathway. Haploid plant carrying n chromosomes is induced via anther culture, isolated microspore culture, ovule culture, or wide hybridization-induced chromosome elimination such as wheat × maize system. Haploid set containing single allele per locus is then doubled chemically with colchicine or spontaneously through endomitosis, producing 2n chromosome complement where both copies are identical duplication of same genome. Resulting disomic is fully homozygous, 100% inbred in one generation, termed true-breeding. Two generations may be needed counting haploid induction plus doubling, but genetic homozygosity per se is achieved immediately upon doubling, without progressive fixation. Breeders obtain stable inbred lines from heterozygous F1 within 12-18 months versus 5-6 years, dramatically shortening breeding cycles in barley, wheat, maize, and vegetables for rapid cultivar release. Flow cytometry and chromosome counting confirm ploidy status after doubling, while molecular markers verify homozygosity absence of heterozygous alleles; DH technology combined with genomic selection and speed breeding forms modern accelerated