The U.S. Department of Justice has established a database that catalogs PCR amplification products from short tandem repeats of the Y chromosome (Y-STRs) in humans. The database contains polymorphisms of five U.S. ethnic groups (African-Americans, European Americans, Hispanics, Native Americans, and Asian-Americans) as well as the worldwide population.

Given that STRs are repeats of varying lengths, for example (TCTG)₉₋₁₇ or (TAT)₆₋₁₄, explain how PCR could reveal differences (polymorphisms) among individuals. How could the Department of Justice make use of those differences?

Key Concepts

Short Tandem Repeats (STRs)

Short Tandem Repeats (STRs) are repeating sequences of DNA that vary in length among individuals. These polymorphic regions are highly variable, making them useful for genetic profiling. The number of repeats can differ between individuals, which allows for the identification of genetic differences that can be used in forensic analysis and paternity testing.

Polymerase Chain Reaction (PCR)

Polymerase Chain Reaction (PCR) is a technique used to amplify specific DNA sequences, making millions of copies of a targeted region. This process involves repeated cycles of denaturation, annealing, and extension, allowing for the analysis of STRs even from small or degraded samples. PCR is crucial for detecting the variations in STRs that can distinguish between individuals.

Forensic Applications of Y-STRs

Y-STRs are specific to the Y chromosome and are inherited paternally, making them particularly useful in forensic investigations involving male lineage. The U.S. Department of Justice can utilize the differences in Y-STR profiles to identify suspects, establish paternity, or resolve cases of sexual assault, where male DNA may be present. This database aids in matching DNA samples to individuals based on their unique STR patterns.