Achromatopsia

Animal arrogance

I beg to differ with the quote, attributed to Ethan Temeles in "Flowers, not flirting, make sexes differ" (SN: 7/22/00, p. 52): "This is the first really unambiguous example of ecology playing a role in the morphological differences between the sexes." The statement exhibits the annoyingly common practice among zoologists to think and generalize as if only animals (and, even worse, only vertebrates) and their literature matter. The plant literature contains numerous published studies, for multiple species, of ecologically driven sexual differentiation and displacement in vascular plants alone.

Michael Grant University of Colorado Boulder, Colo.

Not everything's about sex

Your article "Gene mutation for color blindness found" (SN: 7/22/00, p. 63) ends with the claim that "a color-blind person and a noncarrier have no chance of having a color-blind child." Yet as I recall from basic biology class, color blindness is considered a prime example of a sex-linked trait, which makes the above statement untrue. Carried on the X chromosome, the trait would manifest differently depending on whether the offspring were male or female. Please clarify.

Elizabeth Bakwin Chicago, Ill.

The color-blindness mutation of people on Pingelap is found on chromosome 8. The other known mutation leading to achromatopsia, this form of color blindness, is on chromosome two. While some forms of color blindness are sex linked, this one isn't. --N. Seppa

Tip off the old block

The July 22 cover, "Sticker shock," and the related article ("The little engines that couldn't," SN: 7/22/00, p. 56) say that the powerful forces that arise at the surface of micromachines weren't expected. Any skilled machinist who has used Johannsen gauge blocks in measuring and checking his work would not be surprised at all. These blocks are stacks of hardened steel rectangles with highly polished, flat, parallel surfaces. They are used in the gauging of measurements in precision machining. Because of the precise finish and flatness of the pieces, molecular cohesion forces hold them together in a bond not easily broken. Johannsen gauge blocks have been in use for a hundred years.

Norman MacRitchie Honolulu, Hawaii

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