Question

Describe the role that mobile DNA elements may have played in evolution.

PLEASE cite source(s) and NO wikipedia. thank you!

Answer 1

DNA and Evolution

Deoxyribonucleic acid (DNA) is the blueprint for all inherited characteristics in living things. It is a very long sequence, written in code, that needs to be transcribed and translated before a cell can make the proteins that are essential for life. Any sort of changes in the DNA sequence can lead to changes in those proteins, and, in turn, they can translate into changes in the traits those proteins control. Changes at a molecular level lead to microevolution of species.

The Universal Genetic Code

The DNA in living things is highly conserved. DNA has only four nitrogenous basesthat code for all differences in living things on Earth. Adenine, cytosine, guanine, and thymine line up in a specific order and a group of three, or a codon, code for one of 20 amino acids found on Earth. The order of those amino acids determines what protein is made.

DNA Sequencing and Divergence

Now that DNA fingerprinting has become easier, cost-effective, and efficient, the DNA sequences of a wide variety of species can be compared. In fact, it is possible to estimate when the two species diverged or branched off through speciation. The larger the percentage of differences in the DNA between two species, the greater the amount of time the two species have been separate.

Changes in DNA

All cells are pretty well-equipped with a way to check a DNA sequence for mistakes before and after cell division, or mitosis. Most mutations, or changes in DNA, are caught before copies are made and those cells are destroyed. However, there are times when small changes do not make that much of a difference and will pass through the checkpoints. These mutations may add up over time and change some of the functions of that organism.

Evidence for Evolution

DNA has only come to be understood over the last century. The technology has been improving and has allowed scientists to not only map out entire genomes of many species, but they also use computers to compare those maps. By entering genetic information of different species, it is easy to see where they overlap and where there are differences.

Origin and Evolution of DNA and DNA Replication Machineries

The transition from the RNA to the DNA world was a major event in the history of life. The invention of DNA required the appearance of enzymatic activities for both synthesis of DNA precursors, retro-transcription of RNA templates and replication of singleand double-stranded DNA molecules. Recent data from comparative genomics, structural biology and traditional biochemistry have revealed that several of these enzymatic activities have been invented independently more than once, indicating that the transition from RNA to DNA genomes was more complex than previously thought. The distribution of the different protein families corresponding to these activities in the three domains of life (Archaea, Eukarya, and Bacteria) is puzzling. In many cases, Archaea and Eukarya contain the same version of these proteins, whereas Bacteria contain another version. However, in other cases, such as thymidylate synthases or type II DNA topoisomerases, the phylogenetic distributions of these proteins do not follow this simple pattern. Several hypotheses have been proposed to explain these observations, including independent invention of DNA and DNA replication proteins, ancient gene transfer and gene loss, and/or nonorthologous replacement. We review all of them here, with more emphasis on recent proposals suggesting that viruses have played a major role in the origin and evolution of the DNA replication proteins and possibly of DNA itself.