When two siblings have their DNA tested, the resulting reports usually come back as being similar. However, what a lot of people don’t realize is that two siblings with the same parents can get back different results for their ancestry. This is actually a common occurrence since there are different things that can affect a person’s genealogical ethnicity. Keep reading to learn more.
1. Human Genetics
In order to understand how DNA testing works, you have to know a little about how human genetics work. Here are some basics.
Human DNA is divided into big chunks called chromosomes; humans have 23 pairs of these chromosomes. Most genealogical DNA tests look at the first 22 pairs of chromosomes, which are called autosomes. The twenty-third pair is the sex chromosome and so isn’t tested.
Each chromosome is further divided into smaller pieces called genes. Each chromosome can contain thousands of genes. Genes tell the body how to grow and work. They also control eye colour, complexion, hair colour, and many other things. These genes can help determine a person’s genetic heritage. Some genes are only found in certain ethnic groups, so ethnicity estimates use these genes to see where a person’s ancestors lived.
2. Genetic Mixing
The way that genes are passed from parents to children isn’t straightforward. We each have 22 pairs of autosomal chromosomes but the pairs aren’t identical. A person’s reproductive cells will take pieces from each of these chromosomes to make a unique configuration for each person. The new DNA strand will look very similar to the old one but isn’t identical. This is why siblings can look like each other; however, unless they’re identical twins, there will be differences between their genetic codes.
This means that there could be differences between two siblings’ ethnicity estimates as well.
3. Ethnicity Estimates
In the past, people didn’t move around as much as they do today, and typically married into their own religious or ethnic group. Small pieces of their DNA that identify ancestry accumulated over time. As a result, a person whose DNA ancestry shows one of those little pieces of DNA that only appears among Egyptians, that person very likely had an Egyptian ancestor.
4. Example of DNA Inheritance
If a person’s paternal grandfather is half Scottish and half English, and the paternal grandmother is 100 percent Irish, you may think that the person’s father would be 25 percent Scottish, 25 percent English, and 50 percent Irish, but that’s not always the case.
The paternal grandmother can only pass on her Irish genes, so half of the father’s genes are Irish. But the paternal grandfather can pass on either Scottish or English genes, and not only exactly half of each.
With each generation that goes on, there’s more chances for a completely random number of genes from each ethnicity to be handed down to offspring. After only two generations, two siblings could have some huge differences at their genetic level.
Siblings share around half of their DNA with each other, but some can share more or less.
5. Different Relatives Among Siblings
The way that DNA is jumbled from parents to children means that siblings may also show different relatives. Once a person’s DNA is tested, the results are matched up against everyone else in the database to see if there are relatives. Because one person’s DNA isn’t identical to a sibling’s, their relatives won’t be exactly the same. While siblings may show the same close relatives, the results for their more distant relatives will likely be different.
