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JUNK DNA, REPEATS, TRANSPOSONS AND VIRAL ELEMENTS. “Over evolutionary time, viruses actively exchange genetic material with their host cells. However, just because a non-coding RNA expressed by a virus exhibits hallmarks of a known class of host cell non-coding RNAs does not mean that it necessarily functions comparably. Viruses are extremely clever at altering the bits of host cell genome that they acquire to meet their own needs.” https://lnkd.in/dD7FjZ4 View in LinkedIn

CONSERVED REPEATS. “The telomeres in human cells consist of thousands of repeats of the sequence TTAGGG. This sequence is remarkably conserved from primitive organisms to humans. The sequence is found in all invertebrates and in some trypanosomes and slime molds.” http://protein.bio.msu.ru/biokhimiya/contents/v62/full/62111380.html View in LinkedIn

TELOMERE METRICS. “Harley et al. observed that the mean telomere length decreased by 2 to 3 kilobase pairs (kbp) during the serial passage of several strains of normal human diploid fibroblasts. The decrease was found to be progressive and averaged 50 base pairs for each population doubling. The telomere shortening seen in aging normal human fibroblasts also occurs in vivo in skin epidermal cells, peripheral blood leukocytes and colon mucosa epithelia.” http://protein.bio.msu.ru/biokhimiya/contents/v62/full/62111380.html View in LinkedIn

REPETITIVE DNA. “Telomeres are structures found at the ends of linear chromosomes and consist of repetitive DNA sequences. Telomeres apparently prevent recombination and allow the attachment of chromosome ends to the nuclear envelope.” http://protein.bio.msu.ru/biokhimiya/contents/v62/full/62111380.html View in LinkedIn

JUMPING GENES. “However, in response to a potential decay of the chromatin structure during aging, excess retrotransposon transcription prevents recruitment of cohesion and condensin, causing persistent DNA damage checkpoint activation and senescence.” http://journal.frontiersin.org/article/10.3389/fgene.2013.00136/full View in LinkedIn

SO ENDS this first of two weekends on plant alternation of generations. That such a complex system exists is in part due to the necessity of not increasing chromosome numbers during successive generations, as well as the cobbling together of available tools that were handy. Evolution is a zig zaggy chaotic process with many dead ends and mistakes. Nothing was purpose-built. View in LinkedIn

BACK TO CHROMATIN. “Telomere-mediated activation of the DNA damage response appears to be intimately linked to the chromatin structure. Specifically, it was shown that chronic DNA damage from the processed telomeres also affects histone expression leading to their depletion and to the depletion of the central histone chaperones.” http://journal.frontiersin.org/article/10.3389/fgene.2013.00136/full View in LinkedIn

DIFFERENT HELPER CELL GROUPS. "Depending on their sex and their stage of development, plant reproductive cell lineages are associated with different supporting cell populations. In the stamen, male meiotic cells are invested by a layer of sporophytic (somatic) tapetal cells, which are essential for postmeiotic development and, particularly, the synthesis of the sporopollenin pollen wall and its coating." http://www.sciencedirect.com/science/article/pii/S1534580713000427 View in LinkedIn

TELOMERES AND DNA DAMAGE. “Telomere length is highly connected with the replicative lifespan of metazoan cells. Telomeres shorten with each successive round of DNA replication until one telomere reaches a threshold of “shortness” that emits a chronic DNA damage signal that causes the cell to cease dividing and enter senescence. Mechanistically, the short telomeres are seen as chronic DNA damage by the cell, resulting in the activation of the DNA damage response, which causes a G1 cell cycle arrest.” http://journal.frontiersin.org/article/10.3389/fgene.2013.00136/full View in LinkedIn

OUTSOURCED FUNCTIONS. "It is also evident that certain functions vital for protecting transgenerational genome integrity in animal germ cells, such as the suppression of transposition in the germ cell genome, has been partially “outsourced” to gametophytic helper cells in plants." (Targeted at suppressing parasitic mobile genetic elements by transposing silencing). http://www.sciencedirect.com/science/article/pii/S1534580713000427 View in LinkedIn