9.3 DNA Fingerprinting ppt



Definition of DNA Fingerprint

  • Laboratory technique determining a person’s identity based on unique nucleotide sequences in DNA.

Why is it Called a DNA Fingerprint?

  • The chance of two non-identical twins sharing the same DNA fingerprint is extremely small.

  • Genetic uniqueness allows DNA to serve as a biometric identifier similar to a conventional fingerprint.

  • DNA fingerprinting does not show a person's genotype but indicates the number of repeat sequences, often from non-coding DNA regions.

DNA Fingerprint as a Restriction Map

  • Based on noncoding DNA regions with repeating sequences, where the number of repeats varies among individuals.

  • The resulting banding pattern on a gel forms the DNA fingerprint.

  • DNA samples are placed near the negative electrode on a gel; smaller fragments with fewer repeats migrate further.

Use of DNA Fingerprinting for Identification

  • The probability of DNA match plays a critical role; multiple people may share repeat numbers, but identical matches in several locations is exceedingly rare.

Calculation Example

  • Example involves probabilities related to specific repeat sequences at different DNA locations, demonstrating how to calculate match likelihood.

Applications of DNA Fingerprinting

  • Used in:

    • Criminal case evidence

    • Paternity tests

    • Immigration requests

    • Biodiversity studies

    • Tracking genetically modified organisms

Self-Assessment Questions

  1. True Statements about DNA Fingerprint:

    • It is a type of restriction map.

    • It cannot distinguish among siblings.

  2. Identifying Molecular Differences: The basis for differences lies in noncoding DNA regions.

  3. Pattern of Bands: Reveals the sizes of DNA fragments related to the number of repeat sequences.

Probability Calculation Example - Random Match Probabilities.

  • Probability calculations illustrate how likely two individuals might share DNA traits.

Analysis - Paternity Testing

  • Children inherit half their DNA from each parent; matches between the child’s bands and parental bands help determine paternity.

Crime Scene Analysis

  • Comparing DNA from suspects to a crime scene sample helps identify or exclude potential suspects based on matching band patterns.