Principles & Methods of Germplasm Conservatio

• Chemical Structure of Cytosine: Cytosine is a pyrimidine derivative with an amino group attached at carbon 4 and a carbonyl (oxygen) group at carbon 2 of the heterocyclic pyrimidine ring.
• IUPAC Nomenclature: 4-amino-2-oxypyrimidine (or 4-amino-1H-pyrimidin-2-one). (Correct answer: Option 4)

• Statement (I) is True: Prophase constitutes the longest phase of mitotic nuclear division (often occupying over $50\%$ of total mitotic duration), involving extensive chromatin condensation, sister chromatid resolution, nucleolar disintegration, and mitotic spindle assembly.
• Statement (II) is True: During metaphase, chromosomes attain their highest level of condensation, aligning along the equatorial metaphase plate; because they are at their shortest and thickest, metaphase chromosomes provide optimal clarity for karyotype analysis, ideogram construction, and morphological assessment of centromeres and secondary constrictions.
• Conclusion: Both Statement (I) and Statement (II) are true (Option 3).

Correct option: (3) Statement (I) is correct but Statement (II) is incorrect.

• Assertion (A) is True: Genetic Male Sterility (GMS) lines cannot produce viable pollen and therefore cannot self-pollinate. To maintain the GMS line (female parent), it must be continually maintained by backcrossing with an identical heterozygous male-fertile maintainer line ($Ms/ms$), which yields a 1:1 segregating progeny of fertile ($Ms/ms$) and sterile ($ms/ms$) plants.
• Reason (R) is True: The male sterility phenotype in monogenic GMS is governed by a recessive nuclear gene ($ms$). Because the homozygous recessive genotype ($ms/ms$) is completely sterile and the maintainer parent provides the dominant allele ($Ms$), heterozygous crossing maintains the recessive allele in the population.
• Relationship: Because the recessive nuclear gene ($ms$) governs the phenotype, cross-pollination with heterozygous plants ($Ms/ms$) is biologically mandatory to generate sterile segregants in every maintenance generation. Thus, Reason (R) correctly explains Assertion (A).
• Conclusion: Both (A) and (R) are true and (R) is the correct explanation of (A) (Option 1).

Correct option: (1) Both (A) and (R) are true and (R) is the correct explanation of (A)