英语时差：指纹

Yael: They say that no two fingerprints are alike, but my daughter's fingerprints sure look similar to mine.

Don: While the intricate details of an individual fingerprint are unique, pattern types and the overall size, shape, and spacing of the ridges in a pattern are all inherited traits.

Y: So you mean that my daughter's fingerprints include a lot of whorls because mine include a lot of whorls?

D: You got it.

Y: What kinds of minute details distinguish my fingerprints from my daughter's?

D: To identify the correct person behind a large whorl with wide spacing, one must look at fine details such as slight differences in various landmarks of the whorl pattern, how different ridges break or fork, and the shape of ridge edges.

Y: Okay, but how is it that some features of fingerprints are inherited while these details are not?

D: Because fingerprints are produced by a combination of genetic programming and random chance. Early in gestation, a fetus develops smooth, raised pads on the fingers, palms, and feet. These are called volar pads. At about week ten, these pads cease growing and begin to regress. It may be that the hands continue to grow, resulting in the pads stretching out. Anywhere between about week ten to week fifteen, the early ridges of one's fingerprints begin to form. The ridges appear on the surface of the hand by week sixteen. This timing of ridge formation is one feature that is genetically programmed, and hence, if your parents have a lot of whorls on their fingertips, you're likely to possess a lot of whorls too. However, the intricate details of your whorls are left to chance.