Biosocial Surveys (2008) / Chapter Skim
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9 Are Genes Good Markers of Biological Traits?--Mary Jane West-Eberhard
9 Are Genes Good Markers of Biological Traits?--Mary Jane West-Eberhard
Pages 175-193
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From page 175... ...
I was especially aware that the dramatic differences between sterile social-insect "workers" and egg-laying "queens" do not depend on genetic differences between individuals, but instead spring from differences in their social environments, in particular the dominance relations among adults, and their diets as larvae. From such a background it is clear that phenotypic traits are not determined by genes alone.
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From page 176... ...
on genetic markers in population surveys of human traits whose language could serve as a model of meticulous accuracy in the discussion of genetic data. This chapter is intended as a kind of reader's guide for how to relate genes to phenotypic traits in general, in order to better interpret research results and public discussions that attempt to relate genes to particular human characteristics.
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From page 177... ...
The role of the environment in the induction of genetically complex, reorganized phenotypes, as when fetal undernutrition affects the expression of obesity, diabetes, coronary heart disease, and hypertension in large numbers of adults (Osmond and Barker, 2000) , is a reminder that human populations can contain appreciable frequencies of complex, well-defined phenotypic variants that do not correspond to genetic variants.
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From page 178... ...
In addition to the discrete on-off qualitative traits of organisms, there are other traits, such as body size or longevity, that are "quantitative traits" -- features that are described in terms of their numerically measurable (quantifiable) values (e.g., weight, mass, or life span)
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From page 179... ...
The intertwined genomic and environmental influences on trait expression are further complicated by the fact that previous episodes of gene expression themselves add to the effective environment: genes act within cells, and gene products become part of the internal environment for subsequent gene expression. Previous gene expression and interaction with the environment also contribute to the physical and social environments of any subsequent episode of gene expression.
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From page 180... ...
Trait determination occurs when a new branch is formed at a decision or switch point, depicted here as governed by a threshold that characterizes some environmentally sensitive, genetically influenced developmental mechanism. Alternative pathways lead to alternative phenotypic forms, which involve the expression of alternative sets of genetic modifiers or use of alternative sets of gene products.
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From page 181... ...
Complex off-on traits, as well as quantitative traits, are universally polygenic in both regulation and form, as well as universally environmentally sensitive in their expression. In addition, discrete trait expression involves two major sets of genes: those upstream of the trait, whose expression or products influence whether or not and when the trait is produced; and those downstream of the trait, whose expression or whose products modify the form of the trait itself, rendering it distinctive relative to other traits of the same organism.
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From page 182... ...
gene, and even a graceful jaw gene responsible for a human facial trait not present in other primates. What is the empirical basis for these announcements?
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From page 183... ...
The mosaic or compound nature of the bipolar disease phenotype is indicated by clinical variation in disease symptoms of this and related disorders, which has been referred to as the "bipolar spectrum" (Gershon, 1990, p.
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From page 184... ...
QUANTITATIVE TRAIT MARKERS: LONGEVITY GENES Three of the genes in my collection of genes "for" traits are genes for quantitatively variable traits -- obesity, longevity, and intelligence. The polygenic nature and environmental sensitivity of variation in these traits is so obvious as to need no evidence beyond common experience.
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From page 185... ...
Longevity genes remain the quantitative-trait genes of widest public interest. Not everyone has severely limited intelligence or an obesity problem, but everyone has a limited life span.
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From page 186... ...
lead, we can list the criteria to be satisfied by a dependable single-locus genetic marker of a phenotypic trait: 1. The phenotypic trait whose future occurrence is to be predicted by the marker has to be uniformly and operationally well defined, for example, as a specific measurable value of a quantitative trait or a set of consistently associated distinctive characteristics of a qualitative, discrete trait.
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From page 187... ...
Potential Traps Given the structure of development in relation to gene expression and the polygenic nature of complex traits, there are several kinds of errors likely to appear in discussions of genetic markers and their evaluation by researchers. Type 1 error. The assumption that a gene (a genetic allele)
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From page 188... ...
; masses of protein data generated by automated machines would need to be accompanied by masses of correlated data on polymorphic genotypes, clinically well-defined phenotypes, life stages, and geographic locations of samples to be useful in biomarker research. The pessimistic view presented here regarding single-gene markers need not apply to the search for genetic markers in general.
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From page 189... ...
Good advertising demands nice clean language, so "the obesity gene" or "the gene for alcoholism" readily displaces the more accurate "a gene that influences obesity" or "enhances the likelihood of addiction to alcohol." The public could easily be educated, in classrooms and in the press, to exercise common sense about genetic explanations and to realize that many genes must affect traits like obesity, intelligence, and alcoholism, whose causes are obviously complex. People seem to prefer simple explanations and the promise of simple solutions to complex problems.
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From page 190... ...
. Both facts are explicable by the observation, already mentioned, that it is common to find that ancestral phenotypes, and the underlying genes, have been recombined during evolution in new coexpressed sets to produce novel phenotypic traits.
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From page 191... ...
. Evidence that a single nucleo tide polymorphism in the promoter of the G protein receptor kinase 3 gene is associated with bipolar disorder.
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From page 192... ...
. Biological complexity and strategies for finding DNA variations responsible for inter-individual variation in risk of a common chronic disease, coronary artery disease.
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From page 193... ...
. Multiple-stress analysis for isolation of Drosophila longevity genes.
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