Practice question

Pure line originates from single homozygous plant that through repeated selfing becomes genetically uniform with homozygosity exceeding 99 percent across genome. Starting material may be landrace mixture, segregating population or single heterozygote, but after several generations of single plant selection and self-pollination, locus fixation occurs according to Ht equals H0 half to power t. Johannsen using Phaseolus vulgaris demonstrated selection within resulting pure line does not shift phenotype because variation purely environmental. Molecular markers such as SSR show monomorphic profile within line. Concept fundamental to pedigree method where F2 individual selected and advanced by selfing until F6 to extract superior pure line for evaluation. Pure line provides stable genotype preserving adapted gene complexes and serves as parent for hybrids and multiline blends. 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.