Academic journal article The American Biology Teacher

"Traits Are Not Always What They Seem"

Academic journal article The American Biology Teacher

"Traits Are Not Always What They Seem"

Article excerpt

January's colorful cover (Shields, 2007) of Mendel's classic peas is an appropriate occasion to note the recent identification of Mendel's gene for yellow/green (cotyledon color) in several other species (Armstead et al., 2007). Mendel's I locus seems homologous to "staygreen" (sgr) in meadow fescue (Festuca pratensis) and the model mustard Arabidopsis thaliana, with additional equivalents in maize, sorghum, and rice. The sgr gene helps break down chlorophyll when leaves and cotyledons senesce. Some plants genetically lose that enzymatic function and "stay green" longer. RNA interference (the method recognized in last year's Nobel Prize) was used to silence the gene in Arabidopsis, which exhibited prolonged chlorophyll retention. The discovery may be a reminder that traits are not always what they seem: In this case, the fundamental trait concerns senescent function; seed color is merely expressed pleiotropically.

This discovery also nicely reveals the biochemical basis of a phenotypic trait. As for the biochemistry of the other trait depicted on the cover--round and wrinkled--one may refer to Guilfoile's (1997) informative profile of starch-branching enzyme (SBE1). Here, the biochemical background indicates that the trait may be better described as starchy (round) v. sweet (wrinkled). Biochemical analysis also adds important depth of understanding. For example, heterozygotes for this trait produce an intermediate amount of SBE1. As noted by Darbishire nearly a century ago, hybrids produce starch grains that are also intermediate in size and form. …

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