What's the difference?
I thought that the X and Y chromosomes determined gender in animals, but I see no mention of them in "When to Change Sex" (SN: 1/17/04, p. 40: When to Change Sex). Does this mean that on a genetic basis, males and females in these organisms are identical?
Neil H. Murphy
Walnut Creek, Calif.
In a sense, yes, says Philip Hastings of the Scripps Oceanographic Institute in La Jolla, Calif. Sex-changing fish don't rely on chromosomes to determine sex, so there's no special DNA difference between males and females. However, other fish species, such as swordtails and guppies, do depend on chromosomes to determine sex.—S. Milius
John Harris is quoted as saying that the absence of opossums is a "curious exception" to the list of current mammals of the Los Angeles Basin preserved in the La Brea tar pits ("L.A.'s Oldest Tourist Tra