The numbers and terms

One of the main reasons to perform a DNA test is to confirm and find long lost relatives, whether you knew they existed or not. According to 23andme, their “ability to detect first cousin relationships or closer is approximately 100%.” The following are the types of relationships and the approximate predication rates:

  1. 100%: identical twin
  2. 50%: father, mother, son daughter, brother, sister  
  3. 25%: half-bro/sis, grandpa/ma, grandson/daughter, uncle, aunt, nephew niece
  4. 12.5%: 1st cousin, great-grandpa/ma, great-grandson/daughter, great-uncle/aunt, great-nephew/niece
  5. 3.125%: second cousin – same great-grandparents
  6. 0.781%: third cousin – great-great-grandparents
  7. 0.195%: fourth cousin – great-great-great-grandparents
  8. 0.05%: fifth cousin – gggggrandparents
  9. 0.0122%: sixth cousin – ggggggrandparents

Finding genetic relatives link here 

Cousin relationship Probability of detecting
1st Cousin or closer ~100%
2nd Cousin >99%
3rd Cousin ~90%
4th Cousin ~45%
5th Cousin ~15%
6th Cousin and beyond <5%

Percent DNA Shared by Relationship link here 

Relationship Average % DNA Shared Range [1]
Identical Twin 100% N/A
Parent / Child
Full Sibling
50% Varies by specific relationship
Grandparent / Grandchild
Aunt / Uncle
Niece / Nephew
Half Sibling
25% Varies by specific relationship
1st Cousin 12.5% 7.31% – 13.8%
1st Cousin once removed 6.25% 3.3% – 8.51%
2nd Cousin 3.13% 2.85% – 5.04%
2nd Cousin once removed 1.5% 0.57% – 2.54%
3rd Cousin 0.78% 0.3% – 2.0%
4th Cousin 0.20% 0.07% – 0.5%
5th Cousin 0.05% Variable
6th Cousin 0.01% Variable

Once removed means a generation difference, and twice removed is a two-generation difference:

  • Peter is my mother’s first cousin, who is my first cousin, once removed. It emphases on the relationship between Peter to my mom.
  • Jane is your grandfather’s first cousin, she is my first cousins, twice removed.

My DNA test 我的基因测验

Ok, I finally did a DNA test with a few spits of saliva. It’s super easy.
Here is 23andme’s accuracy rate of correctly predicting relationships (and what they mean).
I’ve long wondered how a person would react upon learning that s/he is likely to develop a certain illness/disease in the future… I guess the test has seen to this, so it asks:
Would you like to receive your health reports? You have the option to check: Yes, No, Ask me again later.

The reports offered are:

Late-Onset Alzheimer’s Disease
Parkinson’s Disease
BRCA1/BRCA2 (Selected Variants)
MUTYH-Associated Polyposis

Then you can configure your reports

Where do you live (country and zip code) matters, as does your race:
Are you Hispanic or Latino? The options are: Yes, No, I’m not sure and more choices going into race.

Regarding your health, they ask: Have you smoked at least 100 cigarettes in your entire life? … and your height, weight, … and if you are a night or morning person …

I’ve dropped it off at the post office, and I anxiously await my report -:). Here is my timeline and their emails, keeping me posted:

  • 7.27, my report came @ 2:25pm EST
  • 7.25, we’re reviewing your genetic data
  • 7.22, we’re genotyping your DNA
  • 7.20, what to expect in your reports
  • 7.19, to their lab, in queue for DNA; be ready by Aug 9
  • 7.17, sent out in the am
  • 7.16, the kit arrives (unreal – so fast!!)
  • 7.15, ordered it on Amazon