Pigmentation Genetics

It seems many people don’t understand basic genetics. At one time, the study of heredity held to the simple idea that hereditary traits are mostly continuous, with offspring being pretty much blends of their parents. However, that idea was pretty much shot down by the work of a certain 19th century monk, showing that heredity occurs in distinct units, genes, of which an organism inherits one copy from each parent, and which interact via various dominance relationships.

Consider, for example, the color of carnations; red, pink, and white. Here, we have incomplete dominance. The gene for color has two alleles: R, which makes red pigment; and R’, which produces no pigment. A carnation with RR is red; that with R’R’ has no pigment, and is white. If we cross-breed these two, all offspring are pink: with genotype RR’, they produce red pigment, but at levels lower than a red carnation, and thus the mixed color. However, breed two pink carnations, and the results defy the pre-Mendel “mixing” theory. Let us draw up the Punnett square:

  R R’
R RR RR’
R’ RR’ R’R’

So, we see that on average, half the offspring will be pink (RR’), but one quarter will be red (RR) and one quarter white (R’R’).

So, with obvious examples like this, why does the idea of the major variations in human pigmentation disappearing via intermixing of the various “races” still seem to persist (this is one of the many pop-culture examples of the idea)? Consider the multiple examples of “different race” twins: see here, here, here, and here.

While human pigmentation is much more complex than that of carnations, it is still due to a finite number of genes, each with a finite number of discrete alleles. Thus, variations in human pigmentation are unlikely to naturally disappear, short of a mass disaster producing a genetic bottleneck.

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One Response to “Pigmentation Genetics”

  1. ahmedseo Says:

    useful info to understant the genetics traits

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