DNA Fingerprinting is a forensic and genetic analysis technique used to identify individuals based on their unique DNA profiles. It relies on the fact that every individual's DNA contains specific regions with varying lengths and sequences, such as repetitive DNA sequences or short tandem repeats (STRs), which are highly polymorphic.
Sample Collection: A biological sample, such as blood, saliva, hair, or tissue, is collected from a person or a crime scene.
DNA Extraction: DNA is extracted from the collected sample using various methods to obtain a pure DNA sample.
Amplification: To ensure that there is enough DNA for analysis, a technique called polymerase chain reaction (PCR) is often used to selectively replicate the specific DNA regions of interest, such as STRs.
Fragmentation: The amplified DNA is then fragmented into smaller pieces using enzymes or other methods.
Electrophoresis: These fragments are separated by size through a process called electrophoresis. An electric field is applied to a gel, causing the DNA fragments to migrate based on their size, with smaller fragments moving faster and larger ones moving slower.
Transfer to a Membrane: After electrophoresis, the separated DNA fragments are transferred to a membrane, typically made of nitrocellulose or nylon.
Hybridization: The membrane is exposed to a DNA probe, which is a labeled segment of DNA that is complementary to the repetitive sequences being analyzed. The probe binds to complementary sequences on the membrane.
Detection: The bound probe is detected, often using autoradiography or other imaging techniques, revealing a pattern of bands on the membrane.
Interpretation: The pattern of bands, known as the DNA fingerprint or genetic profile, is analyzed. Differences in band patterns indicate variations in the repetitive DNA sequences, and each individual's profile is unique.
DNA Fingerprinting Uses-
Forensic Science: To match suspects to crime scene evidence, exclude innocent individuals, and identify missing persons or victims.
Paternity and Maternity Testing: To determine biological parentage accurately.
Genetic Mapping: To locate genes and genetic markers on chromosomes, aiding in understanding genetic diseases and inherited traits.
Population Genetics: To study genetic diversity within populations, track evolutionary processes, and assist in conservation efforts.
Medical Diagnostics: To identify genetic mutations associated with diseases and conditions, including cancer and genetic disorders.
Polymorphism in genetics refers to genetic variation at the DNA level, and it plays a crucial role in fields like genetic mapping and DNA fingerprinting. In simple terms, polymorphism means differences in our DNA that make each person unique. Let's break down the concept of polymorphism step by step.
1. Polymorphism Arises from Mutations:
Polymorphism occurs because of mutations in our DNA. Mutations are changes in the DNA sequence, and they can happen in two main types of cells in our body:
- Somatic Cells: These mutations occur in our regular body cells and are not passed on to our offspring. They can result from various factors, including environmental exposures.
- Germ Cells: These mutations occur in our reproductive cells (sperm and eggs). If a mutation in a germ cell doesn't harm an individual's ability to have children, it can be passed on to the next generation through sexual reproduction.
2. DNA Polymorphism Defined:
- In genetics, we consider a DNA sequence variation to be a polymorphism when more than one variant, called an allele, exists at a specific location in the DNA within a population.
- For a variation to be considered a polymorphism, it needs to be relatively common. Typically, if a variation occurs with a frequency greater than 0.01 (meaning it's found in more than 1% of the population), it's termed a DNA polymorphism.
3. Non-Coding DNA and Polymorphism:
- Many polymorphisms are found in non-coding regions of our DNA. Non-coding DNA doesn't contain instructions for building proteins.
- Mutations in these regions may not have an immediate impact on an individual's ability to reproduce or survive.
- Because these mutations don't have a major effect, they can accumulate over generations, leading to genetic diversity within a population.
4. Types of Polymorphisms:
Polymorphisms come in various forms, ranging from:
- Single Nucleotide Polymorphisms (SNPs): These involve changes in single DNA letters (nucleotides) and are the most common type of polymorphism.
- Insertions and Deletions: These involve the addition or removal of DNA segments.
- Variable Number Tandem Repeats (VNTRs): These are sequences where a small DNA segment is repeated multiple times, and the number of repeats varies between individuals. VNTRs are the basis of DNA fingerprinting.
5. Role in Evolution and Speciation:
- Polymorphisms play a vital role in evolution and speciation. They contribute to the genetic diversity that allows species to adapt to changing environments and can lead to the formation of new species over time.