How Much DNA Do Half Siblings Share?

More people are becoming more interested in their DNA. More people are completing tests such as Ancestry DNA, which  have been growing in popularity over the past couple of years.

This post may contain affiliate links. I will earn a small commission, at no extra cost to you, if you make a purchase through an affiliate link.​

You may have been curious about how much DNA and centimorgan you share with your half brother or sister. Centimorgan is a unit of measurement, which is used to measure genetic linkage.

It is becoming an increasingly common question, how much DNA do I share with my family, as people delve deeper into their DNA. This article will go into further detail about how much DNA half siblings share, so you gain a better understanding.

What is DNA?

DNA (Deoxyribonucleic Acid) is the hereditary material in humans and most organisms. This complex molecule contains all of the information to build and maintain an organism. Every living thing is made up of DNA.

When organisms, such as humans reproduce, a portion of their DNA is passed along to their offspring. DNA in humans decides what sex a person will be, their hair and eye color. It is the structure that says what this person will look like. As DNA is passed down through the generations, this provides continuity within a family, with slight differences over time. 

The DNA molecule is full of a structure called chromosomes. Chromosomes make sure that your DNA is replicated and distributed correctly during cell division. Everyone has 46 chromosomes that are split into 23 pairs.

These chromosomes carry important genetic information that is passed down from parents to children, which helps make people unique. 

What Are Half Siblings?

Half siblings are related through blood by one parent, either their mother or father. They have one parent in common.

Half siblings often are seen as real siblings by most people, because the siblings share some form of biological relationship through the one parent that the siblings share. 

Half siblings are also seen as immediate family members because they share the same genes as one of the parents. Also, some half siblings live together, which can make them have a closer relationship.

Do Half Brothers And Sisters Share The Same DNA?

Full siblings share the same genetic information from the same two people. Compared with half siblings who only share DNA from one parent. Therefore half siblings share only 50% of their shared parents’ DNA.

The DNA that half siblings share won’t be the same, this is because each sibling will inherit a randomly selected half of their shared parents’ DNA. Some of the DNA that has been randomly chosen will match with their half siblings

As a result, half-siblings share a lot less than 50% of their DNA with each other. There is a range of DNA that half siblings share with one another. The average amount of DNA shared between half siblings is 25%. Although it can range from 17 to 34%. This is considerably a lot less than full siblings. 

How Many Centimorgans Do You Share With Your Half Brother Or Sister?

When trying to measure shared DNA, the most useful unit of measurement is centimorgans. Centimorgans measure how much DNA and the length of specific segments you share with your relatives.

In this case, centimorgans will measure how much DNA you share in the length of DNA you share with your shared parent. It is a measurement of probability and the probability of sharing genetic information.

Therefore half siblings only share 25% of their DNA with one another, then they only share around 1300 centimorgans with one another. Compared to full siblings who share 3500 centimorgans with each other.

Are Half Siblings More Related Than Cousins?

On some tests, your half siblings can come up as your first cousins and that is due to the centimorgans you share with one another. They both are in the 1300 centimorgan range. However half siblings are more closely related genetically than cousins.

Half siblings are much closer relatives than cousins. Although half siblings may be closer relatives than your cousins, they both share the same number of ancestors with each other. Yet half siblings do have more DNA with one another than cousins. 

Do Female Half Siblings Share More DNA Than Male Half Siblings?

Half sisters who share the same father will share more DNA between each other than brother-sister half siblings or half sisters who share the same mother. This is due to the fact that half sisters who share the same father will inherit an identical full copy of their father’s X chromosome.

Biological males have an X and a Y chromosome and biological females have two X chromosomes. This is what determines if you will be a boy or a girl. So if female half siblings share the same father, they both have the same X chromosome that their father has passed down to them.

While a half brother with the same father, got his father’s Y chromosome instead of the X. As a result, half sisters who share the same dad have slightly a bit more shared DNA than if a half brother and sister who share the same father.

Final Thoughts

Overall half siblings share a lot less DNA than you may first think. Depending on if you are half brothers or sisters, you share on average 25% DNA with each other.

Half sisters who share the same father may share slightly more DNA with each other than half sisters who share the same mother or a half brother and sister.

As more people look into their family trees and complete DNA tests, more people are surprised to find out how much DNA they share with other members of their family.

DNA is an important part of everyone, as it is the thing that makes people unique and who they are. By being able to trace our DNA also, we are able to see who our ancestors were and what they looked like. Everyone is made up of a little bit of a lot of people but your DNA is always unique to you.