Download GENETICS AND EXPERIENCE WORKING PAPER

THE ISSUE
It is widely believed that one’s abilities reflect both “natural” or “inborn”
influences, typically attributed to genetic or inherited potential, and their
interactions with experience, from prenatal origins to continuing learning in
adulthood. This implies an important role of what is often referred to collectively
as “the environment.” On the other hand, children are often described as
“resilient,” and both fictional and factual accounts stress the achievement of
individuals in overcoming early deprivation or hardships and succeeding in adult
professional worlds. An important issue is how genetics and environment
interact, or how does the individual become a reflection of both her genotype and
her experience?
WHAT SCIENCE TELLS US
Genes are the parts of DNA in the cell that carry the codes for the structure of
proteins. Every cell in the body of an individual, other than reproductive cells,
has the same set of genes. In humans there are estimated to be somewhat less
than 40,000 of such genes; other animals may have more or fewer. Genes are
regulated in their expression, such that any particular gene may be active or
inactive in a cell. If a gene is active, it is expressed in a cell in the form of a
protein. Proteins carry out the basic functions of the cell. Thus the nerve cells, or
“neurons,” of the brain have particular genes activated whose proteins, for
example, comprise the structure of the synapses through which neurons
communicate or synthesize the chemical neurotransmitters used in the
communication process. What makes one type of cell of the body different from
another type is the pattern of gene expression of each cell and hence the
proteins found in each. In contrast to the neuron, for example, a cell in a muscle
would express genes involved in muscle contraction, while a cell lining the inner
wall of the stomach would express proteins involved in the digestion of food.
Differences between humans and other animals and between animals arise to a
large extent from differences in their genes. In some cases, genes encoding the
same protein in different animals may differ in details of the structure of the
protein that they specify; in other cases, genes may be truly unique, such as that
encoding the structure of the venom in certain poisonous snakes. Differences
between individual humans can also arise from differences in the structure of
individual genes or from the presence or absence of genes. Many disabling
conditions result from the loss or functional impairment of a single gene, and the
presence of different forms of a gene can determine the likelihood of developing
conditions such as Alzheimer’s disorder later in life. {examples? FXS?} Likewise,
desirable characteristics can be encoded in particular genes. Many centuries
before humans knew about genes they knew about inheritance of characteristics
and selectively bred domesticated animals such as horses, cattle and dogs that
exhibited characteristics most appropriate to their designated roles; some breeds
of horses were swift and agile while others emphasized the strength necessary to
carry or pull large loads. Dogs could be bred to herd sheep or cattle or to hunt
edible wild birds. So how do genes give rise to such characteristics? These arise
from what the proteins encoded in the genes do at the level of the body’s cells.

Most processes that occur in cells involve multiple proteins and hence the
activity of multiple genes. The creation of a new synapse in development
involves at least several dozen, and possibly hundreds, of genes.

Genes are often involved in more than one cellular process. Genes
involved in muscle contraction also form parts of the synapses that
activate the muscle, and of synapses in other types of cells.

In most cases we are still early in the process of learning the roles of
particular proteins in various cellular processes. We cannot, for example,
specify the majority of the proteins that are involved in making either new
synapses or new memories in the brain.
Genes don’t specify protein structure directly but act through an intermediary,
“messenger RNA” (mRNA), which carries the genetic message regarding protein
structure to specific locations in the cell where the protein is to be synthesized.
Thus some proteins involved in the structure of the synapse can be made locally
at the synapse, while those involved in producing metabolic energy can be made
where extra energy is needed. A gene that is active in the cell is one that is
producing mRNA.

In any given cell, while thousands of genes may be active, thousands of
others are inactive. Genes whose proteins are involved in the general
processes of energy production are active in most of the body’s cells most
of the time.

Genes can be activated by cellular needs; some of the proteins necessary
to digest chemically different sugars are produced via gene activation only
when particular sugars are present.
So how do genes and experience interact? This question is still being answered,
but we do know that synthesis of some proteins can be activated by behavioral
experience. For example, the fragile X mental retardation protein, the absence of
which causes debilitating mental retardation, is synthesized in response to
behavioral experience. Likewise, the protein CREB, which activates genes
thought to be involved in memory, is itself activated by behavioral experience.
Other genes termed “immediate early genes” are activated by behavioral
experience and in turn activate genes that may allow neurons to store
information arising from the experience.

A simple model for how experience interacts with genes to determine the
characteristics of the child or developing animal is that the experience
activates mechanisms in some cells that in turn activate genes either
directly or by altering the synthesis of the proteins that they encode.

Some proteins serve in “signaling pathways” that specify many kinds of
changes within cells. Experience is encoded in neural activity (“action
potentials,” or “nerve impulses”) which is conducted from the sensory
receptors—e.g., in the retina of the eye—to brain structures that, for
example, process the visual information. When the neural activity reaches
synapses in the brain, in addition to triggering nerve impulses in the
postsynaptic neurons, it may activate signaling pathways that can switch
on genes or protein synthesis that may strengthen or stabilize synapses,
altering the brain’s “wiring diagram.”
At the next level—that of the neuron and its connections with others—the
question is how do these experience-gene-protein interactions affect neurons
(and other brain cells) in ways that alter behavioral abilities or tendencies? How
does experience contribute to the functional organization of the brain? This is an
area in which neuroscientists have begun to generate some very interesting
answers.

During particular times during development, which have been referred to
as “sensitive” or “critical” periods, developing animals and humans need to
undergo certain experiences if development is to proceed normally. For
example, experience viewing a patterned visual environment is necessary
to the development of normal visual ability. A kitten, monkey or human
deprived of such experience (in humans, due to extremely poor
uncorrected vision, for example) will have impaired vision even after the
optical deficits are corrected with eyeglasses or surgery.

At a neural level, what happens is (synapse stabilization and elimination)

At a cell-molecular level, what happens is (synthesis of protein; is there a
CREB tie-in to early visual development?)