The Molecular Basis of Evolution

By Christian B. Anfinsen | Go to book overview

chapter 2
GENES AS DETERMINANTS OF HEREDITY

Darwin thought of evolution as a process of adaptation to environment by means of the natural selection of favorable "variations." Within the context of the knowledge of his day he could not, of course, replace the word "variations" with "mutations," since the science of genetics had not yet been invented. However, being a man with a strong urge to tie up loose ends, Darwin suggested that "variations," including those that he felt might be acquired in response to environmental pressures during the lifetime of the organism, were inherited by a mechanism in which all the somatic (body) cells contributed information to the germ cells. We know now that acquired characteristics are not inherited and, with the emergence of genetics, it became possible to speak of the inherited characteristics of an organism (his phenotype) as the expression of the sum of his chromosomal genes (his genotype").* We may now

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It should be stressed that environmental conditions, during development, can exert a profound influence on the phenotypic expression of the genes. A classical example of this is the effect of temperature on the number of eye facets in Drosophila whose chromosomes bear the mutations "low-bar" and "ultra-bar."1 Two organisms with identical developmental potentialities may look or act quite differently, although their respective offspring will be back to the old standard

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