Epigenetics of Reproduction in Animals - Building the Most Complex Structure on Earth - page 86

Epigenetic information is not encoded into a specific structure; hence, it cannot
be transmitted in template mode. Instead, it uses a communicative mode of transmis-
sion. There is no physical correspondence between the neural circuit and the indi-
vidual elements of the cascade or the biological algorithms, let alone the relevant
phenotypic character. Epigenetic information happens, emerges in neural circuits,
and is transmitted when needed. It emerges in the form of electrical/chemical signals
released as the output of the computation of external/internal stimuli in specific neu-
ral circuits. It results from the computational activity of the emergent configurations
neural circuits rather than any permanent structures. It is related to such emergent
configurations, but it is different from them. Chemical signals (epigenetic informa-
tion) released by the activity of neural circuits serve as commands that activate one
of several available signal cascades; namely, the one that can produce the specific
change in the target cells. (For an extensive discussion on the nature and origin of
epigenetic information see Cabej (2012, pp. 39-80) .)
In the organismic hierarchy of control, the genetic control at the molecular level
is subordinate to the epigenetic control, but the latter is not independent of the
former because the genetic system influences the epigenetic control via feedback
loops.
Reproduction in Unicellulars
The mechanisms of reproduction in prokaryote unicellulars are asexual: binary fis-
sion and budding. Eukaryote unicellulars use asexual and sexual reproduction (con-
jugation and sporulation).
Reproduction in Single-Celled Prokaryotes
Prokaryotes (from the ancient Greek προ (pro), before, and καρυ ό ν (karion), ker-
nel), include bacteria. The earliest group of unicellular organisms evolved about 3.8
billion years ago ( Cooper, 2000 ). They are divided into two main groups, Archaea
( Archaeobacteria ) and Bacteria ( Eubacteria ). Prokaryotes have no nucleus, and the
genetic material (DNA) is less organized in chromatin and chromosomes than it is
in eukaryote unicellulars. They have ribosomes and cytoplasmic satellite DNA and
cytoskeleton, but lack membrane-bound organelles such as plastids and mitochon-
dria. Having no separate sexes, bacteria reproduce asexually.
Asexual Reproduction
Asexual reproduction is the primary mode of reproduction in unicellular prokary-
otes. The whole mitotic division in bacteria, and unicellular organisms in general, is
under the epigenetic control of the cytoskeleton (see the section “Control Systems in
Unicellulars” in Chapter 1).