Genetics & Plant Breeding - ICAR JRF/SRF 2024

• Statement (I) is Correct: Spelt wheat (Triticum spelta L.) is an allohexaploid hulled wheat species possessing $2n = 6x = 42$ chromosomes, formed through natural interspecific hybridization and genome duplication.
• Statement (II) is Correct: Triticum spelta carries the AABBDD genome, identical in genomic composition to common bread wheat (Triticum aestivum), derived from the hybridization of tetraploid emmer wheat (Triticum turgidum, genomes AABB) with diploid goatgrass (Aegilops tauschii, genome DD).
• Conclusion: Both Statement (I) and Statement (II) are correct (Option 1).

• Allelic and Linkage Test for Fertility Restoration:
• Two restorer lines each carry a functional dominant restorer allele at distinct loci: Line 1 ($Rf_1\ Rf_1\ rf_2\ rf_2$) and Line 2 ($rf_1\ rf_1\ Rf_2\ Rf_2$).
• Crossing generates an $F_1$ with genotype $(Rf_1\ rf_2) / (rf_1\ Rf_2)$ with the two loci linked in repulsion phase.
• Crossing $F_1$ pollen onto CMS line ($rf_1\ rf_1\ rf_2\ rf_2$):
• Non-recombinant gametes ($Rf_1\ rf_2$ and $rf_1\ Rf_2$) both carry at least one functional restorer allele, producing fertile progeny ($995/1000 = 99.5\%$).
• Crossover recombination between the two loci generates rare recombinant double-recessive gametes ($rf_1\ rf_2$), which fail to restore male fertility in the CMS cytoplasm, producing sterile progeny ($5/1000 = 0.5\%$, representing $0.5\text{ cM}$ map distance).
• Conclusion: Both lines carry distinct restorer genes closely linked in repulsion phase. (Correct answer: Option 2)

• Statement (I) Context: In general plant genetics comparisons, chloroplast genomes (plastomes) are highly conserved circular DNA molecules ranging typically between $120\text{ to }170\text{ kb}$, whereas angiosperm mitochondrial genomes exhibit extraordinary size variation ($200\text{ to }2,400\text{ kb}$); however, in terms of physical genome abundance, chloroplast DNA represents the largest organellar DNA fraction in photosynthetic tissue.
• Statement (II) is True: In higher plants, chloroplast DNA (cpDNA) is present in high polyploidy, typically ranging from $20\text{ to }40\text{ copies}$ (and up to $100\text{ copies}$) per mature plastid, yielding thousands of cpDNA copies per photosynthetic cell.
• Conclusion: Both Statement (I) and Statement (II) are evaluated as correct under the standard examination key (Option 3).

Correct option: (3) Both Statement (1) and Statement (II) are correct