Duplication refers to the process where a segment of DNA is copied, resulting in two or more identical segments within the genome. There are several types of duplications, with tandem and insertional duplications being the most significant. In tandem duplication, the duplicated segment is adjacent to the original segment, while in insertional duplication, the duplicated segment is located elsewhere in the genome, potentially on different chromosomes.
Large segmental duplications, which can range from 10 to 50 kilobases, are less common and typically found in specific organisms. An example of tandem duplication can be illustrated with gene B, where an extra copy appears right next to the original. In contrast, insertional duplication shows gene B located far from its original position, highlighting the diversity in duplication patterns.
Duplications play a crucial role in evolution, particularly in the context of ribosomal DNA (rDNA). rDNA is essential for producing ribosomal RNA, which is vital for ribosome formation. In humans, the abundance of ribosomes in each cell necessitates multiple copies of the rDNA gene; without these duplications, survival would be impossible due to insufficient ribosomes for protein synthesis.
Moreover, duplications can lead to the presence of three copies of an allele instead of the usual two. This additional copy allows for evolutionary flexibility, as the third allele can undergo mutations without jeopardizing the organism's survival. While the original two alleles must remain functional, the third allele is free to evolve, potentially leading to beneficial mutations that enhance the organism's adaptability. This mechanism illustrates how duplications contribute to genetic diversity and evolutionary processes.
