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FRAGMENT FROM NATURE these next two weekends deal with plants as alien creatures with confoundingly complex life styles, such as alternation of generations. Plants asexually make spores, which are single haploid cells (one set of chromosomes, n) that can make another plant when stuck in the ground. They also use sperm and egg to reproduce. But the two are linked: the sexual plant makes an asexual plant (n), and that in turn completes the cycle by making the sexual plant (2n), and each event makes a new generation, by alternating sexual and asexual reproduction. Weird. View in LinkedIn

SOMA VS STEM CELLS. “In mammals with a limited growth phase, telomerase activity in somatic tissues is restricted to stem cell derivatives with high proliferation potential. But other animals, like some fish, grow throughout their life with little senescence. All somatic cells require a high proliferation capacity and telomerase should be active in all cells, irrespective of fish age” http://onlinelibrary.wiley.com/doi/10.1016/S0014-5793(98)01020-5/full View in LinkedIn

NUCLEAR REPLICOMETER. “In early efforts to determine the location of the replicometer, early experiments in which the nuclei of old and young cultured cells were fused to the enucleated cytoplasm of opposite aged cytoplasts revealed that the replicometer was located in the nucleus.” http://protein.bio.msu.ru/biokhimiya/contents/v62/full/62111380.html View in LinkedIn

TICK TOCK. “Eukaryotic chromosome termini consist of telomeres, short sequence repeats. According to the telomere hypothesis, DNA replication leads to telomere shortening, resulting in a cellular mitotic clock. Telomerase resets it by telomere synthesis.” https://lnkd.in/dm7mtBZ View in LinkedIn

EVENT COUNTER MINIMA. “An intracellular counting mechanism must be present. These data included: 1) the Phase III Phenomenon itself; 2) our observation that cryogenically preserved cells "remember" at what doubling level they were preserved; and 3) the enormous literature describing hundreds of biological changes occurring in normal cells well before they lose their replicative capacity.” http://protein.bio.msu.ru/biokhimiya/contents/v62/full/62111380.html View in LinkedIn

ANTITHETICAL THEORY. "The sporophyte originated through the intercalation of mitotic divisions in the zygote before meiosis, resulting in a diploid embryo being retained on a gametophytic thallus; the sporophyte would then gradually evolve from a parasitic dependence on the gametophyte into a dominant, physiologically independent organism. The antithetic theory is supported by the dominance of gametophytes over sporophytes in bryophytes and by the absence of sporophytes in charophyte algae." http://rstb.royalsocietypublishing.org/content/367/1588/508.short View in LinkedIn

SEVERAL APPEARANCES. "Land plants (embryophytes) evolved from freshwater multicellular algae, probably related to the extant charophyte groups Charales or Coleochaetales. An alternation of two multicellular generations has evolved several times in different groups of algae but it appears to have evolved only once in the streptophytes." https://lnkd.in/dNCxaKS View in LinkedIn

FIRST APPEARANCE. "A life history involving alternation of two developmentally associated, multicellular generations (sporophyte and gametophyte) is an autapomorphy of embryophytes (bryophytes + vascular plants). Microfossil data indicate that Mid–Late Ordovician land plants possessed such a life cycle, and that the origin of alternation of generations preceded this date." (450-475 My ago). https://lnkd.in/dF6EXUX View in LinkedIn

HAPLOID-DIPLOID LIFE CYCLE. "Unlike animals, land plants undergo an alternation of generations, producing multicellular bodies in both haploid (1n: gametophyte) and diploid (2n: sporophyte) generations. Plant body plans in each generation are regulated by distinct developmental programs initiated at either meiosis or fertilization, respectively." http://www.sciencedirect.com/science/article/pii/S1534580713000427 View in LinkedIn

TWO GENERATIONS. "Plant reproductive cell lineages thus span two generations, commencing in the sporophyte when cells in the male and female sex organs (stamens and carpels, respectively) enter meiosis and terminating in the gametophyte with the formation of gametes." (Meiosis halves the number of chromosomes, 2n to n to allow both parent genes to participate in the offspring without forever amping up the number of chromosomes in the cell). http://www.sciencedirect.com/science/article/pii/S1534580713000427 View in LinkedIn