Question

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:

(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? Justify your answer.
Human and Rhesus Monkey 
OR

[(ii)] Differentiate between Convergent and Divergent evolution.

Hint:

Greater DNA similarity indicates closer evolutionary relationships. Divergent evolution occurs when organisms evolve from a common ancestor and accumulate differences.

Answer 1

(1) The process is called mutation. It refers to a sudden, heritable change in the genetic material. In this context, it results in the substitution of a new allele from the old one.

(2) The correct answer is (A) — Greater the evolutionary distance, greater are the differences in the nitrogenous bases.
As organisms diverge over millions of years, more mutations accumulate, decreasing the percentage similarity in their DNA sequences.

(3) [(i)] The relationship between Human and Rhesus Monkey belongs to Divergent evolution.
Justification: Both species have evolved from a common ancestor but have accumulated genetic differences over time due to different environmental adaptations and selective pressures. 

OR

[(ii)]

Convergent Evolution	Divergent Evolution
Different organisms evolve similar traits independently.	Related organisms evolve different traits from a common ancestor.
Example: Wings of insects and birds.	Example: Forelimbs of human and bat.