- Given are some statements with reference to the use of genes in plant molecular systematics.
A. mtDNA are not preferred over cpDNA or rDNA because they generally show slow rate of sequence evolution and fast rate of structural evolution.
B. cpDNA are not preferred because of their haploidy, uniparental inheritance, and absence of
recombination among cpDNA molecules.
C. rDNA such as ITS are preferred for their higher evolutionary rates as well as shorter sequence length.
D. rDNA and cpDNA cannot be used simultaneously in molecular systematic since they represent conflicting patterns of inheritance.
Which of the above statements are INCORRECT?
(1) A, C and D (2) A, B and C
(3) A and C only (4) B and D onlyClarifying the Use of Genes in Plant Molecular Systematics: Myths and Facts About mtDNA, cpDNA, and rDNA
Molecular systematics has revolutionized plant taxonomy by providing powerful tools to unravel evolutionary relationships using DNA markers. Among the most commonly used genetic markers in plant systematics are mitochondrial DNA (mtDNA), chloroplast DNA (cpDNA), and ribosomal DNA (rDNA). However, several misconceptions persist regarding their use, advantages, and limitations. Let’s examine some key statements about these markers and identify which are incorrect, clarifying the rationale behind marker selection in plant molecular systematics.
Statement Analysis
A. mtDNA are not preferred over cpDNA or rDNA because they generally show slow rate of sequence evolution and fast rate of structural evolution.
Correct.
In plants, mtDNA evolves very slowly at the sequence level but is prone to rapid structural rearrangements. This makes mtDNA less informative for resolving evolutionary relationships at lower taxonomic levels, so cpDNA and rDNA are often preferred.B. cpDNA are not preferred because of their haploidy, uniparental inheritance, and absence of recombination among cpDNA molecules.
Incorrect.
These features—haploidy, uniparental inheritance (usually maternal), and lack of recombination—are actually advantages of cpDNA as molecular markers. They result in simpler inheritance patterns and make cpDNA ideal for tracing maternal lineages and constructing clear phylogenies. cpDNA is, in fact, widely used in plant systematics for these reasons.C. rDNA such as ITS are preferred for their higher evolutionary rates as well as shorter sequence length.
Correct.
The Internal Transcribed Spacer (ITS) regions of rDNA are popular in plant molecular systematics because they evolve relatively rapidly and are short, making them easy to amplify and sequence. This makes them suitable for distinguishing closely related species.D. rDNA and cpDNA cannot be used simultaneously in molecular systematic since they represent conflicting patterns of inheritance.
Incorrect.
It is common practice to use both rDNA and cpDNA markers together in plant molecular systematics. While they do have different inheritance patterns (biparental for nuclear rDNA, uniparental for cpDNA), this provides complementary information and a more comprehensive understanding of evolutionary history. Their combined use can help resolve complex phylogenetic questions and detect hybridization or introgression events.Summary Table
Statement Correct/Incorrect Explanation A Correct mtDNA evolves slowly in sequence, rapidly in structure—less useful for systematics. B Incorrect cpDNA’s haploidy, uniparental inheritance, and lack of recombination are advantages, not disadvantages. C Correct rDNA ITS regions are preferred for high evolutionary rates and short length. D Incorrect rDNA and cpDNA are often used together; their different inheritance is informative, not conflicting. Conclusion
The incorrect statements are B and D.
The use of cpDNA in plant molecular systematics is favored precisely because of its stable inheritance and lack of recombination, and using both cpDNA and rDNA together is standard practice, not a conflict. Understanding these facts helps researchers select the most informative markers for phylogenetic and evolutionary studies.
Correct answer: (4) B and D only
