मराठी

Molecular (Genetic) Evidences

Estimated time: 6 minutes

CISCE: Class 12

Introduction

Molecular evidence uses DNA, RNA and proteins to show that organisms share common ancestry.
Greater molecular similarity → closer evolutionary relationship; more differences → more distant relationship.

CISCE: Class 12

Universal genetic code

DNA sequence similarity

Closely related species have more similar DNA sequences (e.g., humans and chimpanzees).
DNA comparison is one of the strongest evidences for evolution.

Protein sequence similarity (e.g., cytochrome c)

Proteins with the same function (like cytochrome c) show similar amino acid sequences in different species.
Few differences in sequence → species diverged recently; many differences → divergence long ago.

Molecular clock concept

Assumes molecular changes accumulate at an approximately constant rate over long periods.
Number of differences in DNA/protein can be used to estimate time since two species diverged.

Neutral changes / Neutral theory

Many mutations in DNA or proteins are neutral (neither beneficial nor harmful).
These neutral changes still record evolutionary history and help trace relationships over time.

CISCE: Class 12

Molecular (genetic) evidence supports evolution by comparing DNA, RNA, and protein sequences, showing that organisms with greater similarity are more closely related.
Protein evolution reveals evolutionary relationships, as differences in amino acid sequences (e.g., haemoglobin, cytochrome c) act as molecular fingerprints of ancestry.
DNA and nucleotide sequence comparisons (DNA–DNA hybridisation) measure evolutionary distance between species based on sequence divergence.
The concept of a molecular clock uses the rate of genetic changes to estimate the time since species diverged from a common ancestor.
The neutral theory of molecular evolution (Kimura) states that most molecular changes are neutral and spread by genetic drift rather than by natural selection.
The universal genetic code shared by all organisms strongly indicates that all life evolved from a common ancestral origin.