Full Siblings vs Half Siblings

Did you know that there are specific ways to tell the difference between a full sibling and a half sibling? In simple terms, half siblings share either the same mother or father, while full siblings share both, but it can actually be broken down even further. It all has to do with the number of centiMorgans (cM) shared.

For example, full siblings are expected to share about 2550 cM, while half siblings only share around 1700 cM. So what if you share something in between that… what does that make you?

The answer is simple — full siblings share many fully identical regions (FIRs); fully identical means a segment with a match on both the paternal and maternal chromosomes, so full siblings share about or around 25% of their chromosomes. Half siblings, on the other hand, don’t really have any FIRs of significant size. Exceptions can be made, but regardless, they will always share significantly fewer than full siblings.


This drug test form must be completed before check out. The info is required in order to create your donor pass. A donor pass must be presented at the collection site with a valid photo ID. Once the form is complete, you will be able to proceed and check out. Your donor pass will be emailed to you, in most cases same day, or within 24 hours. ALL DONOR PASSES ARE VALID FOR (7) DAYS. Collection site is selected based on the zip code you provided.

Once the order is submitted there are NO REFUNDS. You can only request an extension or drug test credit in case of cancelation.

Thank You for getting in touch with us!

We'll contact you shortly!