Autosomal DNA statistics

An understanding of autosomal DNA statistics is helpful when trying to understand results from a Family Finder test from Family Tree DNA or a Relative Finder test from 23andMe. Autosomal DNA is inherited from both parents. It is randomly shuffled up in a process called recombination and the percentage of autosomal DNA is diluted with each new generation.

DNA percentages

The following figures show the average amount of autosomal DNA shared with close relatives:

• 50% mother, father and siblings
• 25% grandfathers, grandmothers, aunts, uncles, half-siblings, double first cousins
• 12.5% first cousins, half-aunts/uncles, half-nephews/nieces
• 6.25% first cousins once removed
• 3.125% second cousins, first cousins twice removed
• 0.781% third cousins
• 0.195% fourth cousins
• 0.0488% fifth cousins
• 0.0122% sixth cousins
• 0.00305% seventh cousins (ca 92,000 base pairs)
• 0.000763% eighth cousins (ca 23,000 base pairs)

The percentages can vary. For example, a brother might share 52% of his DNA with one sibling and 47% with another sibling. Because of the random way that autosomal DNA is inherited third, fourth and more distant cousins will not necessarily match you with a Family Finder or Relative Finder DNA test. According to Family Tree DNA's figures the Family Finder test has a greater than 90% chance of detecting a match with a third cousin, but just over a 50% chance of detecting a match with a fourth cousin. In contrast the test will sometimes pick up traces of autosomal DNA from your more distant cousins (for example, fifth cousins and beyond). The chart below (courtesy Dimario, Wikimedia Commons) shows the average amount of autosomal DNA inherited by all close relations up to the third cousin level.

Ranges of percentage of genome in common

Figures from 23andMe's Relative Finder:

• Parent/child: 47.54 (for father/son pairs, who do not share the X chromosome) to ~50%
• 1st cousins: 7.31-13.8
• 1st cousins once removed: 3.3-8.51
• 2nd cousins: 2.85-5.04
• 2nd cousins once removed: .57-2.54
• 3rd cousins: ca .3-2.0
• 3rd cousins once removed: .11-1.32
• 4th and more distant cousins: .07-.5

23andMe Compare Genes function

• Parent-child pairs share between 83.94% and 84.20% of SNPs (50% of DNA in common)
• Siblings share between 83.81% and 87.47% of SNPs (50% of DNA in common)
• Uncle/aunt-niece/nephew pairs share between 78.48% and 79.57% of SNPs (25% of DNA in common)
• Grandparent-grandchild pairs share between 77.96% and 80.59% of SNPs (12.5% of DNA in common)
• First cousins and great uncle/great aunt-grandniece/grandnephew pairs share 75.78% and 77.03% of SNPs (12.5% of DNA in common)
• First cousins once removed share ca 75.5% of SNPs (6.25% of DNA in common)
• Second cousins and first cousins twice removed share ca 75% of SNPs (3.125% of DNA in common)
• Unrelated people of European descent share 73-74.6% of SNPs

Tim Janzen's statistics categorized by genealogical relationship

In order to help people who have taken an autosomal DNA test gain greater insight into the genealogical relationships implied by the resultant data Tim Janzen has created a chart that provides statistical information in various categories. The chart was originally designed for use with 23andMe data but now also incorporates data from FTDNA's Family Finder test. The chart is organized by the degree of relationship, with the most closely related people (parents and children, full siblings) being listed at the top and more distant cousins being listed at the bottom. The statistics are based on information from real people who have been tested by 23andMe and Family Tree DNA and who have a known genealogical relationship to someone else who has also been tested by the same company. Further information can be found on Tim's website.

See also

• Autosomal DNA testing comparison chart
• Family Finder versus Relative Finder
• 23andMe versus deCODEme
• Identical By Descent segment

External links

• What is the probability that my relative and I share enough DNA to be detected by Family Finder? from the Family Tree DNA FAQs
• What's the average % DNA shared for different types of cousins 23andMe FAQ
• Ancestor chart from Hope Carnicle showing all the percentages up to the ninth cousin level
• The same ancestor chart from Hope Carnicle in a diamond shape
• How many ancestors share my DNA? by Luke Jostins on the Genetic Inference blog
• Genealogy relationship chart from About.com
• Cousin relationship calculator from Ancestor Search
• Cousin calculator Free download
• Genetic genealogy and the single segment by Steve Mount