Page 403 - Carrahers_Polymer_Chemistry,_Eighth_Edition

366 Carraher’s Polymer Chemistry

is highly responsive to dopamine. In some preliminary personality studies focusing on the number of
these repeat sequence, it was found, in general, that those with only a few, like one or two, sequences
appeared to be more adventuresome than those with a larger number of repeat sequences. Again,
here we are looking at tendencies that are greatly shaped by our individual circumstances. Behavior
tendencies are also implicated by other monoamines such as norepinephrine and serotonin.
Such wholly caused gene diseases are at one end of the spectrum. More likely, gene composition
declares tendencies, some of these are somewhat random tendencies and others are related to our
lifestyles—both voluntary and involuntary. Thus, single genes that dictate aggression, being good
natured, intelligence, criminals, and so on are not present. Most of our tendencies are just that ten-
dencies, and such tendencies are complex and involve the interaction of many genes and the asso-
ciated proteins as well as external forces and opportunities. Genes in such multiple gene systems
are called quantitative trait loci (QTIs) because they are apt to produce similar behaviors within
different people.
Behavior-related illnesses and patterns, both so-called healthy and nonhealthy, are complex and
involve many factors, including external factors, both learned and simply exposed to factors. As
these studies continue two features are emerging. First, is a tendency (not certainty) for this trait to
be inherited. This tendency is generally greater than is the tendency with respect to physical dis-
ease. Second, environment plays a role. Similar environments produce similar people and different
environments for related people produce different people.
As noted before, there are probably few single gene-associated, monogenic, diseases and most
involve a number of genes. This latter group of diseases is called complex or multifactorial dis-
eases. As noted before, these complex diseases are called quantitative trait locus (OTL) disorders
or diseases.
Similar animal studies are useful in studying such diseases where a so-called similar animal is
available. The term similar animal simply means an animal that contracts the same disease because
of a similarity in the disease-causing gene complex. Because of the similarity found between the
genes between varying species, such similar animals should be available for many of the diseases.
Attention deficit hyperactivity disorder is believed to be related to genes associated with the dopa-

mine system, namely DAT1, DRD4, DRD5. And schizophrenia has been reported linked to genes
on chromosomes 1, 5, 6, 10, 13, 15, and 22. As the human genome map is better understood such
combinations will become more evident. Finding such QTLs is the initial step. Next comes identi-
fying the particular interactions between the QTLs, and between the various proteins produced by
them and finally what, if anything, can or should be done to correct or modify the situation.

The Huntington-related problems, while deadly, are visually simple in relation to some other
gene-related problems. Asthma is a disease that has multiple causes and symptoms and appears
to be the consequence of groups of genes acting in multiple ways, some of which may be posi-
tive and others that cause asthma. Asthma, allergy, anaphylaxis, and eczema are all caused by
mast cells altered and triggered by immunoglobulin-E molecules. I am allergic to certain foods
and used to be to certain plants like rag weed. I outgrew much of the rag weed-like allergies but
retain the food allergies. This is typical; allergies can come and go, are of varying severities, and
can vary with age, sex, and race. While there is evidence to tie asthma to genes, the precise group
of genes remains unknown and surely will be more complex than that of the Huntington-related
diseases.
A brief review of the meiosis process is in order. In the first step, the chromosomes of a cell

containing six chromosomes, three homologous pairs, are replicated and held together at their cen-
tromeres. Each replicated double-stranded DNA is called a chromatid or “sister chromatid.” In the
next step, the three homologous sets of chromatids align, forming tetrads that are held together by
covalent bonding at homologous junctions called chiasmata. Crossovers, recombinations, occur
such that the two tethered chromosomes segregate properly to opposite poles in the next step. This
is followed by the homologous pairs separating and migrating toward opposite poles of the dividing

cells. This first meiotic division gives two daughter cells, each with three pairs of chromatids. The

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