What is the probability that any two humans with the same parents will be identical (other than identical twins) to make an identical zygote?

To calculate the probability that any two humans with the same parents will be identical (other than identical twins), we need to understand the principles of genetics. The genetic makeup of individuals is determined by the combination of genes they inherit from their parents.

Humans typically have two sets of chromosomes—one set from the mother and one from the father. Each parent contributes one copy of each chromosome to their offspring. However, during the process of gamete formation (sperm and egg production), a phenomenon called recombination or genetic shuffling occurs. This process randomly shuffles and exchanges genetic material between chromosomes, resulting in genetic variation among siblings.

In a normal scenario, the probability of two siblings (without considering identical twins) having identical genetic compositions is extremely low. This is because each sibling's genetic makeup is a unique combination of the genetic material inherited from their parents.

The probability of having an identical zygote, where the genetic material is essentially a perfect match, would be significantly lower than the probability of two siblings being genetically identical. Identical twins, for instance, occur when a fertilized egg (zygote) splits into two during early development, resulting in two individuals with identical genetic material. However, the probability of this happening is relatively rare, approximately 0.3-0.4% of all births.

In summary, the probability of any two humans (other than identical twins) with the same parents being genetically identical is very low due to the random assortment and recombination of genetic material during gamete formation.