It is possible for a brother and sister to have different fathers due to a phenomenon known as "heteropaternal superfecundation." This occurs when a woman releases multiple eggs during her ovulation cycle and has sexual intercourse with different partners around the same time. If both partners' sperm successfully fertilize separate eggs, the resulting embryos can have different genetic fathers.
Here's how it can happen:
Ovulation: During a woman's ovulation cycle, typically one egg is released from the ovaries. However, in some cases, multiple eggs can be released during the same cycle.
Sexual intercourse with different partners: If the woman has sexual intercourse with different partners within a short timeframe, each partner's sperm can potentially fertilize a different egg.
Conception: If fertilization occurs with different sperm from different partners, multiple embryos with different genetic makeup (and hence different fathers) can develop in the woman's womb.
Heteropaternal superfecundation is relatively rare, but it has been documented in various instances, particularly in cases of fraternal twins. It can only occur if the woman has multiple sexual partners during her fertile period and releases multiple eggs that get fertilized by different sperm.
It's important to note that while it is biologically possible, such cases are still uncommon. Genetic testing can be done to confirm whether siblings have the same or different fathers, and instances of heteropaternal superfecundation have been confirmed through DNA testing.