Creating Y-STR Database

Question

For a homework assignment, I'm asked to contribute toward the development of a Y-STR database of convicted offenders for the purpose of law enforcement.   

I need to describe at least 2 key attributes to be associated with each profile. I also need to outline a procedure for constructing a ranked list of possible suspects based on at least 1 attribute recorded in the database. I also need to list any major assumptions.

Answer 1

When contributing to the development of a Y-STR (Y-chromosome Short Tandem Repeats) database of convicted offenders for law enforcement, here are key attributes and a procedure to consider:

Key Attributes:

1. Y-STR Profile: The primary attribute is the individual’s Y-STR profile, which consists of a set of numbers representing the number of repeats at specific loci on the Y chromosome. This is unique to each individual and is inherited paternally, making it crucial for tracing male lineages.

2. Associated Information: This includes personal identifiers like name, age, ethnicity, last known address, and the offense for which they were convicted. This helps in contextualizing the DNA data and aids in investigations.

Procedure for Constructing a Ranked List of Possible Suspects:

1. Collection of Y-STR Data: First, ensure that Y-STR profiles from convicted offenders are accurately collected and entered into the database along with the associated information.

2. Crime Scene Analysis: When a crime occurs, analyze the Y-STR profile obtained from biological evidence found at the crime scene.

3. Database Comparison: Compare the crime scene profile with the profiles in the database. Rank the profiles based on the number of matching loci. The more loci that match, the higher the profile is ranked.

4. Threshold for Consideration: Set a threshold for the number of matching loci to consider a profile a potential match. Profiles meeting or exceeding this threshold are flagged for further investigation.

5. Secondary Attributes: Consider secondary attributes like geographic proximity of the offenders’ last known address to the crime scene, age, and other factors to prioritize the list further.

Major Assumptions:

• Accuracy of Profiles: It’s assumed that the Y-STR profiles and associated information in the database are collected and recorded accurately.

• Exclusivity of Database: The database is assumed to be comprehensive for the population of convicted offenders, which may not be the case if not all individuals are sampled or if there are errors in data collection.

• Mutations: The method assumes that Y-STR mutations are rare or consistent enough not to significantly impact the matching process.

• Non-Contamination: The biological evidence collected from crime scenes is assumed to be uncontaminated and correctly attributed to the person of interest.