Genome Organization & Cytogenetics of Crop Pl

• Statement (I) is True: Single cross hybrids ($A imes B$) combine two completely inbred, homozygous lines, maximizing specific combining ability (SCA) and total genetic homogeneity; hence, they achieve the highest theoretical yield potential and absolute uniformity among all hybrid types.
• Statement (II) is True: Double cross hybrids ($(A imes B) imes (C imes D)$) contain broader genetic heterogeneity across individuals, conferring superior developmental homeostasis, wider climatic and edaphic adaptability, and greater buffering capacity against biotic and abiotic stresses compared to uniform single crosses.
• Conclusion: Both Statement (I) and Statement (II) are true (Option 1).

Correct option: (1) Both Statement (I) and Statement (I) are correct

• Diallel Analysis Parameters under Extreme Dispersion (Jinks & Hayman):
• When inbred lines of a cross differ at $k$ loci and positive and negative alleles are in complete dispersion across parents with equal frequencies ($u = v = 0.5$):
• The ratio $\frac{H_2}{4H_1}$ reaches its theoretical limit of 1, indicating symmetrical gene distribution and absence of directional dominance bias. (Correct answer: Option 2)

• Vivek Maize Hybrid 9:
• An extra-early maturing (80–85 days) single-cross hybrid maize variety developed by ICAR-Vivekananda Parvatiya Krishi Anusandhan Sansthan (VPKAS), Almora, Uttarakhand.
• The principal maize breeder who developed and released this landmark hybrid was Dr. V.P. Mani. (Correct answer: Option 3)

• Formula for Number of Possible Double-Cross Hybrids:

• Calculation for $n = 20$ Inbred Lines:

• Breakdown: Number of single crosses is $\frac{20 \times 19}{2} = 190$, and pairing non-parental single crosses gives $\frac{190 \times 153}{2} = 14,535$. (Correct answer: Option 3)