Question

Given below are two statements: Statement (I): All phylogenetic marker genes used for nematode molecular taxonomy are housekeeping genes. Statement (II): All housekeeping genes can be used as phylogenetic markers for nematode molecular taxonomy. In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true.
• B. Both Statement (I) and Statement (II) are false.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

Remember that non-coding ribosomal DNA regions (like ITS) are the primary markers used in nematode taxonomy. Because these are not protein-coding housekeeping genes, they demonstrate that Statement I is false.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Molecular taxonomy and phylogenetics use specific gene sequences to study evolutionary relationships and identify species.
An ideal phylogenetic marker must have a suitable rate of mutation to provide sufficient taxonomic resolution at the desired level (species, genus, or family) and should be easy to amplify using conserved primers.

Step 2: Detailed Explanation:
Let us analyze both statements:
Statement (I):
This statement asserts that all phylogenetic markers used for nematode molecular taxonomy are housekeeping genes.
This is incorrect.
The most widely used markers in nematode molecular taxonomy are ribosomal DNA (rDNA) regions.
These include the Small Subunit (18S), Large Subunit (28S, particularly the D2-D3 expansion segments), and the Internal Transcribed Spacers (ITS-1 and ITS-2).
Ribosomal RNA genes and non-coding spacer regions are structural and regulatory components, not protein-coding housekeeping genes.
Additionally, non-housekeeping mitochondrial genes, such as Cytochrome Oxidase I (COI), are also frequently used for barcoding.
Thus, Statement I is false.
Statement (II):
This statement asserts that all housekeeping genes can be used as phylogenetic markers.
This is also incorrect.
Many housekeeping genes are highly conserved or contain numerous paralogs due to duplication events.
This can lead to challenges in distinguishing orthologs from paralogs, making them unsuitable for phylogenetic analyses.
Furthermore, some housekeeping genes do not evolve at a rate that provides useful phylogenetic signal.
Only a select set of housekeeping genes (such as beta-tubulin, hsp90, or RNA polymerase II) are used as phylogenetic markers.
Thus, Statement II is false.

Step 3: Final Answer:
Both Statement (I) and Statement (II) are false.
Thus, the correct choice is option 2.