in many species. There are an estimated 14,000 copies of Mariner in the human genome comprising 2.6 million base pairs. The first mariner-element transposons outside of animals were found in Trichomonas vaginalis. Mu phage transposition is the best-known example of replicative transposition. In Yeast genomes (Saccharomyces cerevisiae) there are five distinct retrotransposon families: Ty1, Ty2, Ty3, Ty4 and Ty5. A helitron is a TE found in eukaryotes that is thought to replicate by a rolling-circle mechanism. In human embryos, two types of transposons combined to form noncoding RNA that catalyzes the development of stem cells. During the early stages of a fetus's growth, the embryo's inner cell mass expands as these stem cells enumerate. The increase of this type of cells is crucial, since stem cells later change form and give rise to all the cells in the body. In peppered moths, a transposon in a gene called cortex caused the moths' wings to turn completely black. This change in coloration helped moths to blend in with ash and soot-covered areas during the Industrial Revolution. Aedes aegypti carries a large and diverse number of TEs. This analysis by Matthews et al. 2018 also suggests this is common to all mosquitoes. Negative effects Transposons have coexisted with eukaryotes for thousands of years and through their coexistence have become integrated in many organisms' genomes. Colloquially known as 'jumping genes', transposons can move within and between genomes allowing for this integration. While there are many positive effects of transposons in their host eukaryotic genomes, there are some instances of mutagenic effects that TEs have on genomes leading to disease and malignant genetic alterations. Mechanisms of mutagenesis TEs are mutagens and due to the contribution to the formation of new cis-regulatory DNA elements that are connected to many transcription factors that are found in living cells; TEs can undergo many evolutionary mutations and alterations. These are often the causes of genetic disease, and gives the potential lethal effects of ectopic expression. TEs can damage the genome of their host cell in different ways: A transposon or a retrotransposon that inserts itself into a functional gene can disable that gene. After a DNA transposon leaves a gene, the resulting gap may not be repaired correctly. Multiple copies of the same sequence, such as Alu sequences, can hinder precise chromosomal pairing during mitosis and meiosis, resulting in unequal crossovers, one of the main reasons for chromosome