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Biology · 2025 · 4 marks
CBSE 2025 · Region 6 · Set 1 · Q29
Read the following passage and answer the questions that follow. According to evolutionary theory, every evolutionary change involves the…
Read the following passage and answer the questions that follow.
According to evolutionary theory, every evolutionary change involves the substitution of a new gene for the old one and the new allele arises from the old one. Continuous accumulation of changes in the DNA coding for proteins leads to evolutionary differences. The chemical composition of DNA is basically the same in all living beings, except for differences in the sequence of nitrogenous bases. Given below are percentage relative similarities between human DNA and DNA of other vertebrates :
| S.No. | Vertebrates | Percentage similarities |
| 1. | Chimpanzee | $\displaystyle 100$ |
| 2. | Gibbon | $\displaystyle 94$ |
| 3. | Rhesus Monkey | $\displaystyle 88$ |
| 4. | Lemur | $\displaystyle 47$ |
| 5. | Treeshrew | $\displaystyle 28$ |
| 6. | Mouse | $\displaystyle 21$ |
| 7. | Hedgehog | $\displaystyle 19$ |
| 8. | Chicken | $\displaystyle 10$ |
(a)
What is the term used for the substitution of a new gene for the old one and the new allele arising from the old one during evolutionary process?
(b)
Which one of the following holds true for the data provided in the above table ?
(A)
Greater the evolutionary distance, greater are the differences in the nitrogenous bases.
(B)
Lesser the evolutionary distance, greater are the differences in the nitrogenous bases.
(C)
Greater the evolutionary distance, lesser are the differences in the nitrogenous bases.
(D)
Lesser the evolutionary distance, lesser are the differences in the nitrogenous bases.
(c)(i)
To which category of evolution (divergent or convergent) does the following relationship belong to ? Justify your answer. Human and Rhesus Monkey
OR
(c)
(ii)
Differentiate between Convergent and Divergent evolution.
Marking-scheme solution
(a)
Mutation
(b)
A/ Greater the evolutionary distance, greater are the differences in the
nitrogenous bases/ or D/ Lesser the evolutionary distance, Lesser are the differences in the nitrogenous bases
(c)(i)
Divergent Evolution, As both of them diverge from same ancestor and possess
homologous structure.
OR
(c)
(ii)
Divergent Evolution
Convergent Evolution
They have different ancestor
They have common ancestor
They possess homologous
structure
They possess analogous
structure
Organ possesses same
structure but different function
Organ possesses different
structure but same function
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CBSE Class 12 Biology past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.