Academic journal article The American Biology Teacher

Acquired Traits Revisited

Academic journal article The American Biology Teacher

Acquired Traits Revisited

Article excerpt

ABSTRACT

Most biology texts villify Lamarck's concept of "inheritance of acquired characters" and leave the impression that all acquired characters are never transmitted to offspring. However, recent research indicates that this is not true! Some "acquired" traits are inherited. I profile some of these striking cases and their importance for evolution and far understanding a broader epigenetic context for heredity and ontogeny (the emerging field of "evo-devo"). Further; I discuss how such cases, even considered as exceptions, contribute to understanding the nature of science, both the role of general rules in biology and the occurrence of conceptual change, or paradigm shifts.

Key Words: Epigenetics; epigenome; evo-devo; genetic assimilation; Lamarckism, paradigm shift; Weissmanism.

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In the February 2007 issue of The American Biology Teacher, Stern and Ben-Aktva "outline a lesson plan that is designed to challenge one commonly held naive idea, namely the inheritance of acquired traits." The present article suggests (and provides at least partial answers to) the following questions for teachers to consider if they wish to pre pare lessons containing information that goes beyond the content of Stern and Ben-Akiva's curriculum.

* The lesson plan of Stern and Ben-Akiva may leave the reader with the impression that all acquired characters are never transmitted to offspring. Are there any examples of heritable acquired characters? If such examples exist, by what mechanisms can acquired traits become heritable?

* If the effectiveness of natural selection depends on the quantity of heritable phenotypic variation in a population, what mechanisms are known to generate this variation?

* If the inheritance of acquired characters is considered by most biologists to be a relatively rare exception to the general rule that acquired characters are not heritable, what can be learned by devoting class time to such "exceptions"?

* What is the meaning of "evo-devo" and why is it important for understanding modem evolutionary theory?

* National standards for biology curricula recommend that students should learn how science works to generate new knowledge. The history of science reveals that the life of many theories is ephemeral. Old theories are replaced or modified by the discovery of new facts of nature or new ways of interpreting existing facts (National Research Council, 1996: p. 201). This heuristic process is sometimes referred to as a "paradigm shift." Can the study of acquired traits be used to help students prepare their minds for paradigm shifts and improve their understanding and appreciation of science as a way of knowing?

* Epigenetics

An acquired trait develops during the life of an organism as a consequence of a genotype that allows certain unusual environmental factors to modify developmental processes, thus producing a different phenotype than would develop in the normal range of environments (the "norm of reaction"). Epigenetics is a branch of genetics that studies how phenotypic variants arise without changing the nucleotide sequence in DNA. Differential gene action is responsible for cellular differentiation; that is, different groups of genes are "turned on" or "activated" (transcribed into RNA; messenger RNA is translated into proteins) while other groups of genes are "turned off' (inactivated or silenced) in different cell types. Finding the signals that regulate when and where gene products are made and in what quantity is the key to understanding genetics, epigenetics, cellular differentiation, ontogeny, and their interrelationships in modem evolution theory (evo-devo).

We now know that many segments of noncoding DNA (not coding for proteins) contain "RNA-only" genes that can be transcribed into noncoding RNA (ncRNA) molecules but are not translated into proteins. Some of these noncoding RNA molecules (called "short interfering RNA" or siRNA) can suppress translation or promote degradation of specific mRNA molecules (Geddes, 2007; Taubes, 2009). …

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