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X-chromosome testing

From ISOGG Wiki

X-chromosome testing, ranging from about 16,000 to over 28,000 SNPs (Single-nucleotide polymorphism), is included by default in testing done on Illumina's OmniExpress and Global Screening Array (GSA) chips, which includes most popular autosomal DNA tests like those from 23andMe, AncestryDNA, Family Tree DNA's Family Finder test, Living DNA, MyHeritage, and others. See the ISOGG autosomal DNA testing comparison chart.

However, the ways in which information about the X-chromosome is used differ from company to company. For example, 23andMe's Ancestry and Health + Ancestry services count the amount of X-chromosome sharing in the evaluation of total centiMorgans shared between two individuals, while the other testing companies do not. Family Tree DNA reports X-chromosome matches but the matches are only reported if the two people already meet the company's autosomal DNA match threshold. FTDNA reports X-chromosome matches down to 1 cMs, but the vast majority of these are false positive matches. This is clearly evident when comparing the X-matches of a male, whose X-chromosome is naturally phased, with the X-matches of females, whose two X-chromosomes are not phased. X-chromosome data can be independently analysed at GEDmatch, where you can also search for X-matches.

X-chromosome inheritance

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