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.

医師監修監修日：2024年8月5日

岡博史（おかひろし）

医師・医学博士／ヒロクリニック統括院長

YouTubeチャンネルなどを通じて、遺伝子やNIPT（新型出生前診断）についてわかりやすく発信しています。

略歴

1996年慶應義塾大学医学部卒業
2004年慶應義塾大学医学博士号取得
2005年慶應義塾大学皮膚科学教室助手
2008年ヒロ皮フ形成クリニック開業
2009年医療法人社団福美会理事長
2015年医療法人社団福美会理事

資格・所属

CAPラボディレクター
日本皮膚科学会皮膚科専門医
日本医師会産業医
東京衛生検査所指導監督医

発信・関連リンク

この記事は、ヒロクリニックNIPPTの編集・監修体制にもとづき、資格を持つ医師が内容を確認しています。

医師監修監修日：2024年8月5日

堤修一（つつみしゅういち）

医師・医学博士／ヒロクリニック博多駅前院院長

略歴

1993年東京大学医学部医学科卒業
2016〜2019年東京大学先端科学技術研究センター准教授

発信・関連リンク

プロフィール詳細

この記事は、ヒロクリニックNIPPTの編集・監修体制にもとづき、資格を持つ医師が内容を確認しています。

参考文献

Edwards A, Civitello A, Hammond HA, Caskey CT. DNA typing and genetic mapping with trimeric and tetrameric tandem repeats. Am J Hum Genet. 1991 Oct;49(4):746-56.
Beckmann JS, Weber JL. Survey of human and rat microsatellites. Genomics. 1992 Apr;12(4):627-31.
Hearne CM, Ghosh S, Todd JA. Microsatellites for linkage analysis of genetic traits. Trends Genet. 1992 Aug;8(8):288-94.
Jeffreys AJ, Wilson V, Thein SL. Hypervariable 'minisatellite' regions in human DNA. Nature. 1985 Mar 7;314(6006):67-73.
Nakamura Y, Leppert M, O'Connell P, Wolff R, Holm T, Culver M, et al. Variable number of tandem repeat (VNTR) markers for gene mapping. Science. 1987 Mar 27;235(4796):1616-22.