Unsolved: Can DNA help solve the case of a Milwaukee girl missing since 2002?
Alexis Patterson, then 7, disappeared on her way to Hi-Mount School in Milwaukee on May 3, 2002.
The latest season of Unsolved, a true-crime podcast for USA TODAY and the Milwaukee Journal Sentinel, examines the case. The episodes feature exclusive interviews with Alexis' family and more details about the police investigation than have ever been made public. Unsolved is available on all podcast platforms.
One of the main questions explored in Unsolved is whether a woman in Ohio is Alexis. DNA could hold the key to the answer. Here's what to know:
How does DNA analysis work?
In the 1990s, scientists discovered that tiny pieces of chromosomes in DNA repeat in certain places.
Dr. Michael Cox, a biochemistry professor at the University of Wisconsin, told Unsolved that the scientists found examples where the genes only repeated between 10 and 30 times in the human population.
What are alleles in DNA analysis?
The places where those repeats occur on a chromosome are called alleles. Chromosome seven is one of the spots where those repeats occur.
"You inherit these alleles from your father and mother," Cox said. "So you get one from dad and one from mom. So on chromosome seven at this one locus ... you might get a repeat that repeats 12 times (from your mom). And from your dad, you get another chromosome seven and you might get one that repeats 17 times."
How can you use DNA to tell if two people are related?
Having a lot of matching markers does not mean two people are related. The important thing is where those matches occur.
For example, two women would need to have the same marker on the same chromosomes, including chromosome seven, to be mother and daughter.
What did an expert say about the Ohio woman's DNA compared with Alexis' mother?
Fourteen years after Alexis disappeared, a man in Ohio told police and reporters he believed his ex-wife could be the missing girl.
Police in Ohio took a DNA sample from the woman and sent it to Milwaukee via FedEx. Because Milwaukee officers didn’t collect it personally, both the man and Alexis’ mother, Ayanna Patterson, harbored doubts about the results, which were negative for a match.
The Ohio woman's DNA already was on file at a courthouse for an earlier custody case. Ayanna Patterson had used a commercial DNA test kit marketed to grandparents. For Unsolved, a reporter sent both DNA results to Cox, the DNA expert, for his opinion. Unfortunately, the results came back the same: no match between Ayanna and the Ohio woman.
"She's very definitely not her mother," Cox said.
How can DNA be used to help find missing kids?
About 46 million DNA profiles are housed in various databases, and advocacy groups and police are turning to DNA analysis to try to find long-term missing children, according to a USA TODAY investigation.
Dive deeper: Could DNA tests bring home missing kids? Lack of diversity in databases hinders searches
However, police are limited in how and when they can search genetic databases.
There's also a lack of diversity in commercial databases. Communities of color are reluctant to give up DNA samples to commercial companies without strong safeguards around how that material can be used, given the history of racial bias in policing and government surveillance.
Learn more about the Alexis Patterson case by listening to the true-crime podcast Unsolved.
This article originally appeared on USA TODAY: DNA could be the key to solving case of missing Milwaukee girl
