Final answer:
Gene variants arose through mutations, horizontal gene transfer, and gene duplication. These processes contribute to genetic diversity and the evolution of species, leading to traits like different blood types in humans.
Step-by-step explanation:
All variants of genes originally arose through various evolutionary processes such as random mutations, horizontal gene transfer (HGT), and gene duplication. The different variants within a species are due to the specific combination of genes inherited from both parents, and even slight alterations in nucleotide sequences can result in different traits. For example, in humans, three gene sequences code for blood type: A, B, and O, leading to various combinations like AA, AB, or OO, determining an individual's blood type. The emergence of new functions often occurs through gene duplication, where a duplicated gene can evolve independently of the original, potentially leading to new adaptations without the loss of the original function.
Moreover, regulatory interactions such as tRNA mimicry and epigenetic mechanisms likely shaped early genetic machinery, contributing to the diversity of genes. The classical model of clonal evolution, where species evolve and only undergo random mutations, has been expanded to include the significant role of HGT, adding complexity to the evolution of species. This transfer of genes between unrelated species defies the simple tree model and informs our understanding of how genetic diversity is achieved.