STR and Their Use in Paternity Testing

What is STR?

Short Tandem Repeats (STR) are specific types of repeating sequences found in DNA. These sequences are composed of short segments of 2 to 6 base pairs that are repeated in tandem. For example, if the sequence “AGAT” appears repeatedly in a row, it forms an STR. STRs are abundant in the human genome, and because the number of repeats varies between individuals, they are highly useful for personal identification and paternity testing.

Repeat Number and Its Importance

The repeat number of an STR refers to how many times a particular repeating sequence occurs within the DNA. This repeat number varies between individuals and is inherited from parents to offspring. By analyzing these repeat patterns, it is possible to identify genetic relationships.

Use of STR in Paternity Testing

In paternity testing, specific STR markers (loci) are used to create DNA profiles. These profiles are then compared to determine the relationship between the parent and child. The process generally involves the following steps:

Sample Collection: DNA samples are collected from the individuals being tested, typically from parents and child. Common sources include saliva, blood, or oral cells.
DNA Extraction: DNA is extracted from the collected samples.
STR Analysis: PCR (Polymerase Chain Reaction) is used to amplify specific STR markers. The repeat number of these amplified STR markers is detected using fluorescent labels or other methods.
Profile Creation: STR profiles for each individual are created, showing the combination of repeat numbers for each marker.
Comparison and Determination: The STR profiles of the parent and child are compared. If there is a biological relationship, the child’s profile should match at least part of the parent’s profile.

Example

Short Tandem Repeats (STR) and Their Use in Paternity Testing

What are STRs?

Short Tandem Repeats (STRs) are specific types of repeating sequences found in DNA. These sequences are composed of short segments of 2 to 6 base pairs that are repeated in tandem. For example, if the sequence “AGAT” appears repeatedly in a row, it forms an STR. STRs are abundant in the human genome, and because the number of repeats varies between individuals, they are highly useful for personal identification and paternity testing.

Repeat Number and Its Importance

Use of STRs in Paternity Testing

Sample Collection: DNA samples are collected from the individuals being tested, typically from parents and child. Common sources include saliva, blood, or oral cells.
DNA Extraction: DNA is extracted from the collected samples.
STR Analysis: PCR (Polymerase Chain Reaction) is used to amplify specific STR markers. The repeat number of these amplified STR markers is detected using fluorescent labels or other methods.
Profile Creation: STR profiles for each individual are created, showing the combination of repeat numbers for each marker.
Comparison and Determination: The STR profiles of the parent and child are compared. If there is a biological relationship, the child’s profile should match at least part of the parent’s profile.

Example

For instance, consider the STR profiles for a mother and child:

Mother’s STR Marker A Repeat Numbers: 12, 14
Child’s STR Marker A Repeat Numbers: 12, 15

In this case, the child’s repeat number 12 is inherited from the mother, while the repeat number 15 is inherited from the father. By comparing multiple STR markers, paternity can be determined with high accuracy.

High Precision and Reliability

STR analysis in paternity testing is known for its high precision. By using multiple STR markers, the likelihood of misidentification is extremely low. Typically, using 15 to 20 STR markers can achieve a paternity determination accuracy exceeding 99.99%.

Conclusion

The repeat number of STRs plays a crucial role in paternity testing. By analyzing the repeat numbers of STRs in an individual’s DNA, paternity can be determined with high accuracy. Paternity testing is an important tool in forensic science, personal identification, and genealogical research.