Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
DNA Fingerprinting: A technique used to identify individuals based on unique patterns in their sequences, specifically the non-coding, repetitive sequences.
DNA Polymorphism: It is the basis of fingerprinting and genetic mapping. It refers to the occurrence of genetic variation within a population at a frequency greater than at a specific locus.
Satellite DNA: During density gradient centrifugation, bulk forms a major peak, while small peaks are formed by repetitive called satellite . These are classified into micro-satellites and mini-satellites based on base composition ( rich or rich), length of segment, and number of repetitive units.
VNTR (Variable Number of Tandem Repeats): These are mini-satellites used as probes in fingerprinting. The belongs to a class of satellite and shows a very high degree of polymorphism.
The Southern Blotting Technique: The process involves the transfer of fragments from an electrophoresis gel to a synthetic membrane (nitrocellulose or nylon).
Steps in DNA Fingerprinting: (1) Isolation of , (2) Digestion of by restriction endonucleases, (3) Separation of fragments by electrophoresis, (4) Blotting, (5) Hybridization using labeled probe, and (6) Detection of hybridized fragments by autoradiography.
📐Formulae
💡Examples
Problem 1:
In a forensic investigation, is extracted from a blood stain (Sample ) found at a crime scene. Two suspects, and , have their analyzed. The patterns show that Sample matches Suspect at all loci tested. What is the probability that this match is coincidental, and what is the biological basis for this match?
Solution:
The probability of a coincidental match is extremely low, often calculated as in or more depending on the number of loci. The biological basis is the unique distribution of (Variable Number of Tandem Repeats) which are inherited from parents.
Explanation:
Since are highly polymorphic and individual-specific (except in monozygotic twins), the identical banding pattern on the autoradiogram between Sample and Suspect confirms the identity of the individual at the crime scene.
Problem 2:
A child's paternity is in question. The mother has alleles of sizes and at a specific locus. The child has alleles of and . What must be the profile of the biological father at this locus?
Solution:
The biological father must possess the allele.
Explanation:
According to Mendelian inheritance, a child receives one allele from each parent. Since the child has (from the mother) and alleles, the allele must have been inherited from the father.