Question

Which aspect forms the basis of DNA finger- printing?

• A. The amount of DNA found in samples of blood, saliva and skin.
• B. The ratio of purines and pyrimidines present in DNA.
• C. The Sequence of DNA present in the ridges and grooves of finger-prints
• D. The Satellite DNA showing high degree of repetition in DNA segments

Answer 1

The Correct Option is D

DNA fingerprinting, also known as DNA profiling or genetic fingerprinting, is a technique used to identify and analyze unique patterns in an individual's DNA. It relies on the presence of specific regions in the genome that exhibit high levels of repetitive DNA sequences known as satellite DNA. These repetitive sequences, such as short tandem repeats (STRs), are unique to each individual (except identical twins) and can be used to distinguish one person's DNA from another.

The process of DNA fingerprinting involves several key steps:

Isolating DNA: DNA is extracted from a sample, such as blood, saliva, or skin cells.

Amplifying DNA: Specific regions of the DNA containing repetitive sequences are amplified using polymerase chain reaction (PCR).

Analyzing DNA fragments: The sizes and patterns of the amplified DNA fragments are analyzed. This is often done using techniques like gel electrophoresis, which separates DNA fragments based on their size.

By comparing the DNA fragment sizes and patterns between different individuals, it is possible to determine if they share a common genetic profile or if they are different.

Therefore, it is the repetitive sequences, particularly satellite DNA regions, that serve as the basis for DNA fingerprinting and enable the identification and differentiation of individuals based on their unique genetic profiles.

Answer 2

Let's analyze each option to determine the correct basis for DNA fingerprinting:

• "The amount of DNA found in samples of blood, saliva, and skin": While having enough DNA is necessary for DNA fingerprinting, the *amount* itself isn't the basis of the technique. The analysis relies on specific sequences within the DNA, not the quantity. Therefore, this is incorrect.
• "The ratio of purines and pyrimidines present in DNA": The ratio of purines (adenine and guanine) to pyrimidines (cytosine and thymine) is generally constant in DNA (Chargaff's rules). This is a fundamental property of DNA structure but doesn't provide the individual variation needed for DNA fingerprinting. Therefore, this is incorrect.
• "The Sequence of DNA present in the ridges and grooves of finger-prints": The ridges and grooves of fingerprints are epidermal features determined by skin structure, and do not reflect the DNA sequence. DNA for fingerprinting is extracted *from* cells left behind in a fingerprint, but it's not the sequence *within* the ridges themselves that's analyzed. Therefore, this is incorrect.
• "The Satellite DNA showing a high degree of repetition in DNA segments": Satellite DNA consists of repetitive DNA sequences found in specific regions of the genome. These sequences, particularly variable number tandem repeats (VNTRs) and short tandem repeats (STRs), exhibit a high degree of polymorphism (variation) between individuals. This variation forms the basis for DNA fingerprinting, as the number of repeats at these loci differs significantly from person to person. These differences create unique DNA profiles. Therefore, this is correct.

Therefore, the correct answer is: The Satellite DNA showing a high degree of repetition in DNA segments.