The Family Finder test works by comparing your autosomal DNA to that of other people in our database who have taken the test. The program calculates your relationship with a match based on sharing linked segments of DNA. Any two people from the same population may share some DNA. However, as matching segments of DNA become longer and as you share more segments, it is unlikely to be a chance match. The sharing is due to a recent common ancestor.

RSID,CHROMOSOME,POSITION,RESULT
"rs12209455","6","112510","AG"
"rs6596790","6","114141","CC"
"rs1535051","6","125959","AA"
...

The Family Finder test process starts with a microarray chip. It returns results for about 690,000 pairs of data points on your 22 pairs of autosomal chromosomes. Note that we do not use the two sex chromosomes for Family Finder analysis. The data points, single nucleotide polymorphisms (SNPs), are variants in the human genome. You inherit each pair with one value that comes from your mother and another that comes from your father. As it is not possible to tell which value comes from each parent, the program reports the values in a standard order, i.e., if it reports a SNP’s values as AG, the A could come from either parent.

The program then organizes results sequentially by their location on the autosomal chromosomes.

SNPs Sets on Chromosome 6
SNP
Set
centiMorgans (cM) Start Stop
2006 0.952442803 112510 402747
2007 0.42626673 405732 667716
2008 0.730014591 667957 942118
2009 0.682739434 943062 1102946
2010 0.748474474 1106892 1306843
2011 0.846707416 1306995 1524189
2012 0.807514144 1525402 1525603
.
Matching on Chromosome 6
Name SNP Set
. 2
0
0
4
2
0
0
5
2
0
0
6
2
0
0
7
2
0
0
8
2
0
0
9
2
0
1
0
2
0
1
1
2
0
1
2
2
0
1
3
2
0
1
4
.
Half Identical Region Match Non-Match
Peter Wiscured
Cousin

The Family Finder software clusters the SNPs into sets that are about 50 to 100 SNPs long. The bioinformatics team has predefined the SNP sets based on contributing SNPs’ reliability, variability, average centiMorgans (cM), density, and other statistical considerations.

For example, the SNPs Sets on Chromosome 6 chart on the left shows seven SNP sets with their start point and stop point.

The software next evaluates SNP sets for matching. They may either be half identical or a nonmatch. A half-identical match means that one of the values for each SNP is a match between the two samples. No calls (where the test did not return clear data) and the potential for random miscalls are taken into account in the match process.

For example, the Matching on Chromosome 6 table on the left shows Peter Wiscured matches a cousin on SNP set blocks #2006 through #2011. The SNP Sets on Chromosome 6 table shows that #2006 starts at 112510 and that #2011 ends at 1524189.

The program then analyzes adjacent SNP sets to see if they qualify as identical by descent (IBD) segments. The DNA Segment is considered IBD if it contains at least 500 SNPs, and it is at least 1 cMs long.

Using Peter Wiscured and his cousin’s match again, their shared segment on Chromosome 6 from SNP set #2006 through #2011 is a total of 4.39 cM (4.386645448 rounded to two decimal places) long. It is then an IBD segment.

The program uses the number, size, and total size of shared DNA segments to determine how recently any two people are related.

Note: The bioinformatics team periodically reviews the start and stop points for the SNP sets. They may differ from the examples.