Practice question

R-line known as restorer line harbors dominant restorer of fertility genes Rf encoding pentatricopeptide repeat proteins targeted to mitochondria where they bind and cleave aberrant ORF transcripts such as orf79 associated with WA cytoplasm in rice, restoring normal oxidative phosphorylation and ATP supply for anther development. Genotype RfRf, cytoplasm may be either S or N but crucial nuclear contribution dominates. Cross between A-line rfrf and R-line RfRf produces F1 heterozygote Rfrf where restorer protein suppresses sterility causing ORF, enabling normal pollen development and full male fertility in commercial hybrid crop for grain production. Strong restoration required across diverse environments, selection uses molecular markers tightly linked to Rf3 and Rf4 loci on rice chromosomes 1 and 10 facilitating breeding of effective restorers with good combining ability. This understanding supports competitive exam preparation for NEET, GATE and CSIR NET concepts linking genotype with phenotype through molecular pathways involving transcription factors, hormones and metabolic enzymes that regulate development, adaptation and reproductive biology in applied breeding programs.