AAMC sample test B/B #37

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AAMC sample test B/B #37

Post by Amber9 » Thu Sep 05, 2019 2:44 pm

I don't understand why the green cones will be strongly stimulated when the red pigment is absent based on the graph

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Re: AAMC sample test B/B #37

Post by NS_Tutor_Mathias » Mon Sep 09, 2019 6:30 pm

Table 1 gives another hint about this question: The "red pigment absent" phenotype corresponds to a genotype that suggests that a dominant allele for a complete lack of red pigment is present. So we can rule out any answer choice that involves seeing red at all already (B&C).

D also suggests something impossible, namely that green pigment would be absent as well: We know that not to be true, so we can rule out this option.

Finally, for A, you just want to realize that light that normally would have activated predominantly photoreceptors featuring red pigment (let's call them red receptors) and to a lesser degree green receptors can now only activate green receptors. This light is still of a wavelength that we would call red - it is still red light - but it will appear green to the person with "red pigment absent". Like the start of the passage says: Such individuals can only absorb for transduction light of two colors (obviously they can still absorb light of any wavelength on non-photoreceptive surfaces, like the entire rest of their body).
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