Transposable Genetic Elements
Transposable genetic elements (TEs) are segments of DNA that can be integrated into new chromosomal (genomic) locations either through direct DNA transfer (transposons), or via an RNA intermediate (retrotransposons). Pseudonyms for TEs include mobile elements, jumping genes, genomic parasites, and selfish DNA. TEs are known to be responsible for several human genetic diseases and may play a role in evolution in many species.
Early Evidence
Barbara McClintock originally theorized that unusual patterns of phenotypic variance (in corn kernels) could be explained by gene transposition. However, this explanation did not coincide with traditional Mendelian inheritance that genetic information was fixed within the genome, and her views were not widely accepted within the scientific community until the 1960s, when evidence of transposition began to accumulate.
McClintock was a cytogeneticist working on maize. She noted that, in maize, there was a pigment-bearing layer of the kernel, called the aleurone layer, that changed color from kernel to kernel and generation to generation. She also noted a baffling result that occurred when a homozygous plant for purple aleurone (CC) was crossed with a colorless aleurone homozygote (cc). About one-half of the kernels of offspring corn were solid purple, and one-half were purple with varying sizes of colorless spots, suggesting breakage (and loss) of the C locus.
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