Yes, two siblings can have different biological parents and still be full siblings, also known as "biological siblings." This situation can occur through a process called "heteropaternal superfecundation." It happens when a woman releases multiple eggs during ovulation, and she has sexual intercourse with two different partners in a short period, leading to fertilization of each egg by sperm from different fathers.
Here's how it works genetically speaking:
Multiple Eggs Released: Normally, during the menstrual cycle, a woman releases a single egg (ovum) for potential fertilization. However, in some cases, two or more eggs may be released during a single ovulation event.
Multiple Partners: If a woman has sexual intercourse with multiple partners around the same time, the sperm from each partner can fertilize different eggs.
Conception: If two different partners' sperm fertilize two separate eggs, two embryos with different genetic material are formed.
Different Fathers: Each embryo, having been fertilized by a different father's sperm, will have a different set of genetic material inherited from their respective biological fathers.
Birth: The two embryos develop independently in the mother's womb and are born as separate babies, making them full siblings with different biological fathers.
Heteropaternal superfecundation is relatively rare but has been documented in scientific literature and paternity cases. With advancements in genetic testing, it is now possible to determine the biological parentage accurately, which has revealed some cases of siblings with different fathers.