The possibility of two non-twin individuals having the same genome is extremely low due to the vast number of potential genetic combinations possible. Identical twins have the same genome because they come from the same fertilized egg. The genetic uniqueness of each person is influenced by a combination of many factors, including single nucleotide polymorphisms and the resulting genetic variation.
Uniqueness of the Human Genome
The human genome comprises over three billion pairs of bases, containing the genetic material necessary to encode a human being. Each human couple has the potential to produce over 64 trillion genetically unique children due to the various mechanisms of genetic variation. This ensures that, unless they are identical twins stemming from the same fertilized egg, it's almost impossible for two people to have exactly the same genome by chance alone.
Identical twins are an exception as they inherit copies of the exact same chromosomes and thus have the same genes. However, for two non-twin individuals to have identical genomes, the odds are exceedingly low due to the high number of possible genetic combinations. In fact, the genetic variation brought about by single nucleotide polymorphisms (SNPs) and other genetic mechanisms contributes to the uniqueness of each individual, affecting traits as diverse as susceptibility to diseases and physical characteristics.
While it is theoretically possible for two non-twin individuals to have the same genome given a sufficiently large population, the actual probability is so small that it doesn't generally occur in the human population. To put it in perspective, there are currently about 7 billion humans, which is far less than the number of potential unique genetic combinations that humans can produce.