36. Somatic recombination was caused by mild exposure to radiation on flies heterozygous for a given allele during specific stages of development and the individuals were allowed to develop. Such individuals are likely to have
A. clones of homozygous cells in heterozygous body.
B. site specific mutagenesis.
C. twin spots, i.e., patches of mutants cells and homozygous wild type cells in heterozygous body.
D. tissue specific expression of the given allele.
Which of the following combination of answers will be most appropriate?
(1) A and B (2) B and C
(3) A and C (4) C and D
Somatic recombination induced by mild radiation exposure in heterozygous Drosophila flies during development produces clones of homozygous cells and twin spots in the heterozygous body. The correct combination is A and C.
Question Breakdown
The query describes flies heterozygous for an allele (e.g., +/m) exposed to mild radiation at specific developmental stages, triggering somatic recombination via mitotic crossing over between homologous chromosomes. Post-recombination, during mitosis, daughter cells segregate to yield homozygous +/+ and m/m clones amid the heterozygous tissue; these proliferate into visible patches due to clonal expansion in imaginal discs. Radiation promotes double-strand breaks repaired by homologous recombination, a classic Drosophila assay.
Option Analysis
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A. Clones of homozygous cells in heterozygous body: Correct. Mitotic recombination in G2 phase of a heterozygous cell generates homozygous daughter cells (+/+ and m/m), which divide mitotically to form clones distinguishable by phenotype in the surrounding heterozygous tissue.
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B. Site specific mutagenesis: Incorrect. Mild radiation causes random DNA damage, not targeted to specific sites like CRISPR; it induces general recombination or mutations without locus specificity.
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C. Twin spots, i.e., patches of mutant cells and homozygous wild type cells in heterozygous body: Correct. Twin spots are adjacent +/+ (wild-type) and m/m (mutant) clones from X-segregation post-recombination, often seen in wing or eye discs as paired patches; Z-segregation yields single homozygous clones.
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D. Tissue specific expression of the given allele: Incorrect. Recombination alters genotype mosaically, not expression patterns; phenotypes reflect homozygous vs. heterozygous states, independent of tissue-specific regulation.
Correct Answer
Option (3) A and C best describes outcomes, as confirmed in CSIR NET contexts and Drosophila genetics literature on radiation-induced mosaics.
