32. Which of the following statements about R-banding chromosomes is FALSE?
(1) The heat treatment preferentially denature the GC rich DNA to produce R-banding pattern.
(2) This is essentially the reserve of the G-banding pattern.
(3) The R bands are Q (quinacrine) negative
(4) The DNA of R bands generally replicate early during the S-phase of cell cycle
R-Banding Overview
R-banding produces a reverse pattern to G-banding on chromosomes through heat denaturation in phosphate buffer followed by Giemsa staining, highlighting GC-rich regions as dark bands. These bands correspond to euchromatin areas near telomeres, aiding detection of terminal chromosomal abnormalities. R-bands generally replicate early in the S-phase due to their gene-rich nature.
Option Analysis
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Option (1): Heat treatment preferentially denatures AT-rich (not GC-rich) DNA, allowing GC-rich regions to stain darkly with Giemsa; GC-rich DNA has higher melting temperature (~105°C) and remains stable. This statement is false.
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Option (2): R-banding is the reverse of G-banding, where R-dark bands match G-light bands and vice versa.
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Option (3): R-bands are Q-negative, as quinacrine staining targets AT-rich regions that appear pale in R-banding.
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Option (4): R-band DNA replicates early in S-phase, consistent with active euchromatin properties.
R-banding chromosomes false statement analysis reveals key cytogenetics facts for exams like CSIR NET Life Sciences. This technique uses heat treatment on metaphase chromosomes to denature AT-rich DNA, producing dark GC-rich R bands as the reverse of G-banding patterns. Understanding R-banding chromosomes false statement helps clarify mechanisms: option (1) wrongly claims GC-rich DNA denaturation, while correct details cover Q-negative staining and early S-phase replication.
