Should other family members get their DNA tested?

The short answer is, yes. To understand why other family members should have their aDNA tested, let’s review how genes get passed down. (For more detailed information, you can read about genetic inheritance.)

DNA Match Ancestry Confirmed

You and your 5th cousin have the same 4th great-grandparents. For you to have a DNA match with that cousin, the same section of DNA would have to be passed down through six generations to both of you. Since DNA recombination is a random process, there may be no common DNA inherited by both of you (see Figure 1).

Figure 1. An inheritance chart showing why you and some of your distant cousins may not be DNA matches.

 

Table 1 shows how likely you are to have a DNA match with a cousin. As you can see, you may have a known cousin—and perhaps a shared ancestor in a DNA Circle—but no DNA evidence to support your relationship.

Relationship Likelihood of a DNA Match
Siblings 100%
1st cousins 100%
2nd cousins 100%
3rd cousins 98%
4th cousins 71%
5th cousins 32%
6th cousins 11%
7th cousins 3.2%
8th cousins 0.91%
Table 1. The likelihood that you and a distant cousin have matching DNA.

Figure 2. An inheritance chart showing how a close relative may have a DNA match with a distant cousin when you do not.

Table 2 shows how likely it is that your close family members would have a DNA match with a cousin that you don’t share DNA with. Keep in mind that if the cousin is on your father’s side of the family, the close family member (like your brother or aunt), must also be on your father’s side of the family.

Distant

Relationship

Sibling Uncle/

Aunt

Niece/

Nephew

Parent Grand-

parent

First

Cousin

Second

Cousin

3rd cousins 87% 99% 64% 96% 100% 94% 97%
4th cousins 42% 78% 25% 63% 92% 57% 64%
5th cousins 15% 37% 8% 26% 58% 22% 26%
6th cousins 4% 13% 2% 9% 23% 7% 8%
7th cousins 1.5% 4% 0.8% 3% 8% 2% 3%
8th cousins 0.43% 1.23% 0.23% 0.81% 2.3% 0.65% 0.77%
Table 2. The likelihood that a close relative on one side of your family has a DNA match with a distant cousin on the same side of the family, even if you don’t have a DNA match.

It’s important to remember that some of your close relatives, like your nephew or half-sister, have some ancestors that you don’t, which means their DNA matches along family lines that you don’t share aren’t relevant to you in general.


This was copied from dna.ancestry.com where you can order an aDNA test. If you are a Rofheart/Rofes or Jones cousin and order a test, email me at dna@evananda.net so that I can integrate your test into the family tree at ancestry.com.

 

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