Month: September 2022

DOUBLE FERTILIZATION. "As implied by the name, the gametophyte generates the gametes, two sperms in the male pollen and a single egg in the female embryo sac." Both sperms are used in a double fertilization event -- one for the egg cell (to make a diploid zygote) -- and the other for the megamametophyte (to make a triploid nucleus of the endosperm). Wow. 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

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

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

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

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

ANCIENT GENE RECRUITMENT. "One prediction that can be made from the antithetic theory is that the evolution of the sporophyte involved the recruitment of ancient genes and regulatory networks from the pre-existing gametophyte generation; these networks would then diversify and promote morphological diversification in the sporophyte generation." Supported by transcriptomic studies. http://rstb.royalsocietypublishing.org/content/367/1588/508.short View in LinkedIn

RADIATION BY EXAPTATION. "The elaboration of the sporophyte generation, and particularly the large radiation of morphological forms during the Devonian period, was partially achieved through the recruitment of genes and genetic mechanisms that had previously evolved and functioned in the gametophyte generation of charophytes and early land plants." http://rstb.royalsocietypublishing.org/content/367/1588/508.short View in LinkedIn

GENERATION-SPECIFIC GENES. "Some genes also have ancient functions that are restricted to the diploid phase of the life cycle (zygote and/or sporophyte). Some genes have ancient functions that are exclusive to either the sporophyte or the gametophyte generation." http://rstb.royalsocietypublishing.org/content/367/1588/508.short View in LinkedIn

DIFFERENT EVOLUTIONARY PATHS. "The developmental changes involved in the alternation of generation represent the major gene-switching events in the life history of plants. While a large number of genes are common to both sporophyte and gametophyte, many thousand sequences are specifically expressed in each generation; indeed, certain key constituents (e.g. tubulin) are encoded by different genes in each generation, indicating that sporophyte and gametophyte are responding to different evolutionary pressures." https://lnkd.in/d7TmtBz View in LinkedIn