The mixture of breeding lines having the same genetic constitution, but differing at a specific locus is known as

Correct option is A

✅ (a) Multi-lines [Genetic Uniformity with Minor Variation] • Multi-lines consist of several pure lines (genotypes) that are genetically identical except for specific genes (usually disease resistance). • These lines differ at only one or few loci while maintaining overall genetic uniformity. • Commonly used in self-pollinated crops like wheat and barley. • Offers durable resistance against diseases like rusts due to gene diversity.
❌ (b) Recombinant inbred lines • Developed by repeated selfing of F2 individuals to reach homozygosity. • Differ at multiple loci, not just one specific gene.
❌ (c) Iso parental lines • Not a widely accepted or clearly defined term in plant breeding. • Ambiguous in scientific literature.
❌ (d) Doubled haploid lines • Derived from haploid cells doubled to form homozygous diploids. • Genetically uniform at all loci, not differing at any particular locus.