🚨 UPSC EXAM NOTES presents the March edition of our comprehensive monthly guide. Access it  to enhance your preparation. We value your input - share your thoughts and recommendations in the comments section or via email at Support@upscexamnotes.com 🚨

Critical Topics and Their Significance for the UPSC CSE Examination on March 25, 2025

Daily Insights and Initiatives for UPSC Exam Notes: Comprehensive explanations and high-quality material provided regularly for students

What are DNA polymorphisms and how do they differentiate between people?

For Preliminary Examination:  mRNA, DNA

For Mains Examination: GS III - Science & Technology

Context:

Just like the government uses an Aadhaar number to uniquely identify an individual for social security purposes, a person’s DNA fingerprint can be used for biological purposes. This is why DNA analysis is such a big deal. Today, it is most often (but not exclusively) used together with technologies like PCR, capillary electrophoresis, and fingerprinting

Read about:

What is DNA?

• Every cell in the human body—including those in the skin, blood, teeth, and bones—contains 46 DNA molecules. These molecules are inherited in two sets: 23 from the father through sperm and 23 from the mother via the egg.
• Unlike other cells, sperm and egg cells carry only a single copy of the genome rather than two. This fundamental characteristic enables the creation and application of DNA fingerprints for identifying individuals and their relatives.
• Within the cell, DNA is compactly arranged into chromosomes. For instance, chromosome 3 holds 6.5% of the total DNA content. The chromosome 3 inherited from the father is mostly similar to the one from the mother, except for certain variations known as polymorphisms.
• These DNA polymorphisms help distinguish one individual from another. They also reveal whether chromosome 3 from the father was inherited from his mother or father, and the same applies to the maternal chromosome. Such variations allow for tracing ancestry.
• Typically, DNA profiles are constructed using specific polymorphisms found in regions of DNA called short tandem repeats (STRs).

What are STRs?

• DNA consists of two strands, each composed of a sequence of four chemical bases: adenine (A), cytosine (C), guanine (G), and thymine (T). These strands are arranged in an anti-parallel manner, meaning they run in opposite directions.
• They are also complementary, as adenine pairs with thymine and cytosine pairs with guanine. During cell division, the strands separate, and new complementary strands are formed, ensuring that the daughter cells inherit the same genetic sequence.
• Occasionally, errors occur during this process, leading to mutations. However, such mutations are rare, typically occurring less than once per billion base pairs per generation.
• An STR is a short sequence of DNA base pairs that repeats multiple times, such as GATCGATCGATC. On the complementary strand, this sequence appears as CTAGCTAGCTAG. STRs are highly variable among individuals, meaning unrelated people usually have different numbers of repeat units in certain STR regions.

How is DNA copied?

• To analyze DNA effectively, scientists need to produce multiple copies of specific STR regions. This is accomplished through a laboratory technique called Polymerase Chain Reaction (PCR), which can amplify a selected DNA segment of up to 5,000 base pairs, even from a minimal initial sample.
• The process begins with extracting DNA from a biological sample, such as tissue. The sample is then heated to approximately 95°C for 25 seconds to separate the DNA strands.

• ---

  Share to Social

  ---