STUDY OF CHROMOSOMES (Syllabus: GS Paper 3 – Sci and Tech)

Context: A recent study revealed the rapid evolution of the Y chromosome, showing that only 14-27% of ape Y chromosome DNA sequences are similar to those in humans. This suggests a much faster evolutionary rate for the male sex chromosome.

Key Points of Study

• Chromosome Similarity: Over 90 percent of ape X chromosome sequences align with the human X chromosome, showing relative stability in evolution.
• Recent Divergence: Some ape species diverged from the human lineage only seven million years ago, a brief period in evolutionary terms, indicating rapid evolution of Y chromosomes.
• Previous Characterisation: Prior to this study, the sex chromosomes of our closest relatives, non-human apes, were only partially characterized, whereas human sex chromosomes had been fully sequenced.
• Divergence of Orangutans and Chimpanzees: Bornean and Sumatran orangutans diverged from each other approximately 1 million years ago, while chimpanzees and bonobos diverged around 2.5 million years ago. 

o Human lineage divergence from ape lineages occurred roughly 7-20 million years ago.

• Use of Computational Tools: Scientists used a computational tool known as alignment to identify chromosomal regions that have remained relatively unchanged throughout evolution, providing insights into evolutionary pressures on the genome.

Difference between DNA, Gene, and Chromosome

• DNA: It is the molecule that carries genetic information for the development and functioning of an organism. 

o DNA is made of two linked strands that wind around each other to resemble a twisted ladder a shape known as a double helix.

o Composition: It is made up of four letters, representing four chemicals: Adenine, guanine, cytosine and thymine. 

o The DNA palindromes can be over one hundred thousand letters long. 

• The DNA palindromes on the primate X and Y chromosomes almost always contain genes, a unit of heredity passed from parent to offspring.
• Gene: It is considered the basic unit of inheritance.

o Transmission: Genes are transmitted from parents to offspring, shaping the genetic makeup and influencing traits in the offspring.

o Coding for Proteins: Most genes encode for specific proteins or segments of proteins, serving diverse functions essential for cellular processes and overall bodily functions.

• Chromosome: These are thread-like structures located inside the nucleus of animal and plant cells. 

o Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA).