Q.27 The lack of linear correlation between the genome sizes and genetic complexities among various
species is known as
(A) C–value paradox (B) Genetic diversity (C) G–value paradox (D) Central dogma
The correct option precisely describes the observed discrepancy where genome sizes vary widely across species without matching their genetic or organismal complexity.
Option Analysis
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(A) C-value paradox: Refers specifically to the lack of linear correlation between haploid genome size (C-value) and organismal complexity, as seen in cases like amphibians having larger genomes than humans despite lower complexity.
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(B) Genetic diversity: Describes variation in alleles and genes within populations or species, enabling adaptation but unrelated to genome size versus complexity mismatch.
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(C) G-value paradox: Involves the absence of strict correlation between gene number (G-value) and complexity, such as nematodes having similar gene counts to humans.
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(D) Central dogma: Outlines unidirectional genetic information flow from DNA to RNA to protein, a core molecular biology principle with no connection to genome size variation.
The C-value paradox genome sizes genetic complexities puzzle challenges the expectation that more complex organisms possess larger genomes. Observed since the 1970s, this phenomenon shows species like some salamanders with 40 times more DNA than humans, yet simpler traits.
Causes of the Paradox
Genome expansion arises from non-coding DNA, including repetitive sequences, transposons, and polyploidy, rather than gene addition for complexity. Eukaryotes accumulate “junk” or selfish DNA without boosting functional genes.
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Single-celled protists often exceed human genome size due to repeatomes.
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Prokaryotes maintain compact genomes tightly linked to complexity.
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Cell size and nuclear volume correlate more with C-value than gene function.
Examples Across Species
Amphibians exemplify the paradox with oversized genomes from endoreplication, while birds show streamlined ones via selection pressures. Plants frequently undergo whole-genome duplications, bloating C-values without proportional complexity gains.
Resolution and Modern Views
Alternative splicing, regulatory elements, and nucleoskeletal DNA explain why complexity emerges from gene regulation, not sheer size. The paradox persists as a debate on “economy” versus evolutionary drift.
For CSIR NET Life Sciences aspirants, mastering C-value paradox genome sizes genetic complexities aids questions on genome evolution and molecular biology.
