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Genetic information
provided by genes determines the primary structure of proteins,
according to the genetic code, but there is no evidence that it
might also determine the spatial and temporal arrangement of cells
in the developing metazoan structure. Besides, the total amount of
information contained in the genome of higher vertebrates amounts to
a few billion bits, while the total amount of information necessary
for erecting a vertebrate structure, i.e. for determining the
spatial arrangement of billions to trillions of cells of several
hundred different types is more than one million times greater.
Q: If the
genetic information of the genome is qualitatively inappropriate and
quantitatively insufficient what is then where the huge amount of
information for molding the metazoan structure comes from?
A: The early
development from zygote (egg cell in parthenogenetic organisms) to
the phylotypic stage is determined not by zygotic genes but by the
epigenetic information provided by parent(s) to gametes (egg cell
and sperm cells) in the form of parental cytoplasmic factors in a
strictly determined spatio-temporal order. That information
regulates the spatiotemporal expression pattern of zygotic genes up
to the phylotypic stage.
Q: Where
the epigenetic information for the spatio-temporal order of
placement of parental factors in gametes comes from?
A: There is evidence suggesting that
this epigenetic information flows down from the CNS to gametes via
specific signal cascades by utilizing and modifying the structure of
microtubules and cytoskeleton of the gamete (see chapter 4 of the
Epigenetic principles of Evolution).
Q: At the
phylotypic stage the epigenetic information provided by gametes is
exhausted and/or its function terminates. What is the source of the
huge amount of epigenetic information necessary for the
postphylotypic development, organogenesis and morphogenesis?
A: Adequate
empirical evidence on post-phylotypic development shows that the
development of various organs in metazoans depends on CNS signals or
signal cascades originating in the embryonic CNS, the brain or the
spinal cord (see chapter 6 of Epigenetic Principles of Evolution),
clearly suggesting that the embryonic CNS is the source of the
epigenetic information determining organogenesis and individual
development in general.
Q:
Qualitatively new characters in cases of developmental plasticity
involve no changes in genes. Since the development of new characters
requires investment of new information, what is the origin of that
epigenetic information?
A: Solid
evidence shows that developmental changes that lead to the
appearance of qualitatively new characters within the lifetime of
individuals, i.e. without changes in genes, result from activation
of signal cascades that start with brain signals, implying that the
brain is the source of the epigenetic information determining the
new characters (see chapter 11 of the Epigenetic Principles of
Evolution).
Q: During
transgenerational developmental plasticity (TDP) the offspring of
individuals that experienced the action of specific environmental
stimuli develop new characters involving no changes in genes.
Moreover, these new characters are transmitted over generations just
like evolutionary changes. What is the source of the epigenetic
information that makes this epigenetic inheritance possible?
A: Based on
experimental evidence from the studied cases of TDP, it may be
concluded that the epigenetic information for this epigenetic
inheritance originates in the CNS. That evidence has made possible
reconstruction of a generalized mechanism of induction of the TDP
which looks as follows: the specific environmental stimulus is
received by sensory neurons, and converted into electric spike
trains that are processed in specific neural circuits. The
processing of the stimulus, which is a computational non-genetic
process, generates information in the form of a chemical output
(neurotransmitter, neuromodulator, etc.) that is released on
specific secretory neurons, which, in turn secrete a neurohormone
that starts the signal cascade for deposition in the gamete of a
parental factor that determines the development of the new
phenotypic character in the offspring (see chapter 12 of the
Epigenetic Principles of Evolution).
Q: Is
there any essential difference between the mechanism of the TDP (transgenerational
developmental plasticity) and the evolutionary change?
A: No (if
evolutionary change implies the appearance in successive generations
of a new character that the parent(s) lacked).
Q: Where
is the epigenetic information for inducing inherited changes in the
offspring during the transgenerational developmental plasticity
stored?
A: In a few
cases it has experimentally been determined that the information for
activating signal cascades inducing inherited changes is generated
(not stored) in the CNS by processing particular environmental
stimuli in neural circuits whose chemical output (neurotransmitter
or neuromodulator) activates the signal cascade that enables
deposition of a specific factor in the egg cytoplasm (see chapter 12
of Epigenetic Principles of Evolution).
Q: Is
there any verified case of a particular gene whose change is
causally related to a specific change in morphology?
A: No.
Q: Are
there cases of evolutionary changes determined by epigenetic
mechanisms?
A: All the
evolutionary changes described in chapter 14 of the Epigenetic
Principles of Evolution (pp. 379-500) involve no changes in
genes and are epigenetically determined.
Q: What do
these epigenetic mechanisms consist of?
A: Epigenetic
mechanisms determining evolutionary changes described in chapter 14
involve changes in the patterns of expression of genes (but not
changes in genes themselves) involved in signal cascades determining
development of specific characters. The information necessary for
the activation and changes in the expression patterns of genes in
the signal cascade originates in the CNS [this seem to have been the
case in the evolution of the body size in laboratory strains of
Manduca sexta, evolution of wings in insects, evolution of caste
polymorphism in some insect species, evolution of horns in beetles,
evolution of dentition in vertebrates, evolution of plumage
dichromatism in birds, evolution of alternation of sexual and
asexual generations in crustaceans, evolution of flight in insects,
evolution (evolutionary acquisition and loss) of vocal learning in
birds, evolution of migration light-dependent magnetic orientation
etc.].
Q: Is
speciation a cause or a result of evolutionary change and phenotypic
diversification?
A: While
allopatric speciation, formation of new species may result from
geographic isolation of two groups of an original population,
speciation occurring in sympatry may be a cause and a
mechanism of evolutionary change and phenotypic diversification.
Q: If
reproductive isolation of two populations is a necessary condition
of speciation, spatial (geographic) isolation of two populations
seems to be indispensable for speciation. How can reproductive
isolation of populations occur in sympatry, under conditions of
random mating?
A: Metazoans
have evolved neurocognitive mechanisms that make assortative mating
possible in sympatry.
Q: Does
this imply that geographic isolation is not necessary for formation
of new species.
A: Yes.
Q: What is
the epigenetic mechanism of reproductive isolation of two groups of
an original population in sympatry?
A: It is a
neuro-cognitive mechanism that enables a group of individuals of a
population to recognize and preferably mate only with individuals of
the opposite sex in sympatry displaying a particular sensory
(visual, auditory, olfactory, electric behavioral) character. This
implies the occurrence of a change in a sensory signal of the sender
(most commonly males) and a corresponding change in the receiver’s
(commonly females) mate preference for that signal, but involves no
changes in genes of the sender or the receiver.
Q: An
anticipated argument against the epigenetic origin of that mechanism
would be that changes in sender’s signals and respective changes in
receiver’s mate preferences are ultimately determined by genes.
Is this not true?
A: This
conventional guess is not true. All the known changes in sender’s
signals (visual, olfactory, acoustic, electric, behavioral) involve
neither changes in existing genes (gene mutations) nor evolution of
new genes but only changes in expression of existing functionally
unchanged genes. As for the corresponding changes in the
receiver’s mate preferences, they result from changes in properties
of respective neural circuits, which also are not related to any
changes in genes.
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