![Q.15 Amino acid sequences of cytochrome e and ribulose S-phosphate epimerase from 40 organisms were chosen and phylogenetic trees were obtained for each of these two protein families Determine the correctness or otherwise of the following Assertion [a] and the Reason 1 Assertion (a): The two trees will not be identical Reason (r): The nature and frequency of mutations in the two families are different (A) Both [a] and are true and [r] is the correct reason for [a] (B) Both [a] and [r] are true but is not the correct reason for [a] (C) Both [a] and [r] are false. (D) [a] is false but [r] is true](https://www.letstalkacademy.com/wp-content/uploads/2026/01/slide_15-11.png)
Q.15 Amino acid sequences of cytochrome e and ribulose S–phosphate epimerase from 40 organisms were chosen and phylogenetic trees were obtained for each of these two protein families
Determine the correctness or otherwise of the following Assertion [a] and the Reason 1
Assertion (a): The two trees will not be identical
Reason (r): The nature and frequency of mutations in the two families are different
(A) Both [a] and are true and [r] is the correct reason for [a]
(B) Both [a] and [r] are true but is not the correct reason for [a]
(C) Both [a] and [r] are false.
(D) [a] is false but [r] is true
Cytochrome c and ribulose-5-phosphate epimerase phylogenetic trees from 40 organisms are expected to match because both proteins evolve according to the species tree in standard analyses. The assertion claims they will not be identical, but this is incorrect for orthologous proteins across the same organisms. The reason about differing mutations is true but does not explain non-identity here.
Question Breakdown
Amino acid sequences from cytochrome c (likely “cytochrome e” is a variant or typo for the standard cytochrome c used in phylogeny) and ribulose-5-phosphate epimerase (RPE, a Calvin cycle enzyme) were analyzed from 40 organisms to build separate phylogenetic trees. These trees reconstruct evolutionary relationships based on sequence similarities, assuming neutral evolution tracks species divergence.
Option Analysis
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(A) Both true, [r] correct reason: Incorrect. Assertion [a] is false as trees for orthologs from the same organisms should be identical or highly congruent under clock-like evolution.
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(B) Both true, [r] not reason: Incorrect. [a] false; while mutation rates differ (cytochrome c evolves slowly, conserved; RPE faster, metabolic), trees still match species phylogeny.
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(C) Both false: Incorrect. [r] true—different proteins have distinct mutation natures/frequencies due to functional constraints.
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(D) [a] false, [r] true: Correct. Trees will be identical reflecting species tree; mutation differences do not cause topology mismatch in such setups.
Cytochrome c ribulose-5-phosphate epimerase phylogenetic trees from 40 organisms form a classic assertion-reason question in GATE Biotechnology, testing evolutionary biology concepts. This analysis decodes why the trees match, aiding IIT JAM and GATE BT aspirants in mastering cytochrome c ribulose-5-phosphate epimerase phylogenetic trees.
Core Concept
Phylogenetic trees built from orthologous protein sequences (like cytochrome c, a mitochondrial electron carrier, and RPE, a pentose phosphate pathway enzyme) across the same 40 organisms should mirror the species tree. Differences arise only from phenomena like horizontal gene transfer or rate heterogeneity, not expected here.
Why Assertion Fails
Assertion [a] (“trees not identical”) ignores that sequence divergence reflects shared species history, yielding congruent topologies despite length variations.
Reason Validity
Reason [r] holds: Cytochrome c has low mutation frequency (highly conserved); RPE shows higher variability as a housekeeping enzyme. Yet, this affects branch lengths, not tree shape.
Correct Answer: (D) – Matches GATE BT 2020 patterns where species trees dominate. Practice similar questions for bioinformatics sections.
