How Much DNA Do Family Members Share? (With Cousin Relationship Chart)

Artwork © Can Stock Photo / kgtoh

How much DNA do you share with your blood relatives?  Want to know HOW you are related to your cousin?  Here’s some data about genetic sharing among family members, including a cousin chart to help you figure out your family relationship.

When people are related, they share kinship with the other person and are descended from the same common ancestor.  This means that blood relatives are direct descendants of a common ancestor, known as consanguinity. Consanguinity means related by blood, from the Latin consanguinitas, meaning “blood relation.”  But how much ‘blood’ do you really share with your family members?


How to Calculate Family Relationships From A Common Ancestor

When a common ancestor is known, you can use the following chart to determine the cousin relationship between two blood relatives.

  1. You must already know the common ancestor BEFORE using this chart.
  2. Find the FIRST person’s relationship to the shared relative.  For example, the grandchild of the shared relative.
  3. Find the SECOND person’s relationship to the shared relative. For example, the great grandchild of the shared relative.
  4. The intersection of the row and column shows the relationship between the two blood relatives.

In our example, the grandchild and great grandchild are first cousins once removed, as shown on the red intersection of the chart.

CHART: How to Calculate Cousin Relationships with a Shared Blood Relative

Click here to download a pdf printable of Cousin Relationship Chart.

How Are You Related? Try Our Online Family Relationship Calculator.

Find your family relationship with our handy online calculator, based on the above chart.

How Genetically Related are My Family Members?

Now that you’ve found your cousin relationship, how related are you really?

Blood relatives share common DNA which they inherited from a common ancestor.  However, each generation shares LESS genetic material, the further away they are from the common ancestor. This is because with each generation, new genes are brought into the hereditary line, with each birth of a new child.


CHART: Average DNA Shared Between Relatives

Source: 23andMe.com|Retrieved March 2018

GRAPH: Shared DNA Declines With Each New Generation

Distant relatives actually share very little DNA in common.  So even if you are directly descended from George Washington, you really only share very little — almost no — DNA with him!


How Much DNA do Family Members Share?

DNA is inherited randomly; therefore, although each child inherits 50% of their DNA from each parent, but which 50% they inherit can vary greatly. You may randomly inherit more DNA from one side of your family tree, than from the other.  This is why you may look more like grandpa, than grandma!

Remember that the shared DNA numbers are averages. It’s actually possible for you not to share any DNA with a given relative beyond about second cousins — you may randomly inherit more DNA from the other side of your family tree.

Notice that once removed cousins, whether ascendant or descendant, share the same amount of DNA on average.  This is why they have the same given genealogical name, though they are separated on different generational levels of the chart.

Read more about cousinship naming and ascendant/descendant cousins at A Simple Family Relationship Chart for Naming Kinfolk.

Chart: Genetic Relationships Between Blood Relatives

Click here to download a printable version of Genetic Relationships Between Family Members Chart.


Do Siblings Have the Same Ancestry DNA?

Wondering, whether you and your sister have the same DNA?  Remember, siblings share about 50% of their genetic makeup.  This means, unless you have an identical twin, your siblings and parents are the closest DNA match to you.

When you inherit DNA from your parents, you randomly will receive 50% from each parent, but this does not mean you and your sibling will get the SAME 50% from each parent.

So, while you share half of your DNA with your sibling, the OTHER 50% can vary.  No wonder you and your sister are SO very different!