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Transcript
151 Chapter 8 Canalization, Cryptic Variation, and Developmental Buffering 2.6 Mean eye score 2.4 2.2 2.0 1.8 1.6 1.4 C T Allele E1564 E5144 FIGURE 8-6. The effects of genetic background on single nucleotide polymorphism affects. The mean effect of substituting one allele for another depends heavily on genetic background. Not only is the mean effect on photoreceptor determination different for these two crosses, but there is evidence for a large scaling difference of the substitution of alleles. threshold either hides the variation (for invariant traits) or sets up a situation where a quantitative gradient is interpreted digitally (dichotomous). If we return to the results for photoreceptor determination (Dworkin et al., 2003), we can see some results consistent with this as well. Figure 8-6 displays a reaction norm profile across two different alleles for mean eye roughness for the two different crosses employed in this study. Not only does the cross utilizing line 1564 have a greater mean trait value than 5144, but as can be seen, there is evidence for a cross-X polymorphism effect, given that the slopes of the two lines are different from one another. This also points out another important feature. Even though crosses with line 5144 are sufficient to reveal some cryptic genetic variation for eye roughness, in general it produced much lower levels of between-line (genetic) variation. Thus the breakdown of the canalization is not an all or nothing proposition, and (at least for some traits, such as photoreceptor determination) there is a degree to its effects.
