HEY COUSIN In fact, the process lays your two #5 chromosomes side-by-side, like two strands of yarn. It then cuts them crosswise into matching pieces and swaps the pieces between strands. Imagine that the DNA strand from your father was red, say, and your mother’s strand was blue. The cut-and-swap process (called meiosis) with just two cuts would yield one strand that was blue-red-blue and another that was red-blue-red. Many cut-and-swaps later, each new patchwork #5 then goes into a different gamete. And so, the single #5 chromosome in each gamete winds up being a mix of material from your mother’s #5 and your father’s #5. Only thus can your child inherit your mother’s eyes and your father’s chin. The single #5 in the gamete is not a “blend” in the sense of being purple (the combination of blue and red). Instead, it resembles a barber pole with broad blue and red stripes. The width of the stripes is called “linkage disequilibrium.”<quoted text>
Jew-boy! Jew-boy! Come home right now or I'll send Lassie out after you!
As explained in the essay Afro-European Genetic Admixture in the United States, markers throughout the genome can be used to distinguish African from European ancestry. A first-generation Afro-European biracial individual will have one purely African chromosome #5 (from one parent) and one purely European chromosome #5 (from the other). But the strands are cut and their pieces swapped in meiosis at each subsequent generation. So if you observe that an individual has barber-pole stripes of African and European DNA within the same strand, then he must be at least a second-generation biracial. Now the chance that, in the next generation, any given cut will just happen to hit the seam between two existing stripes is negligible. Consequently, the stripes of African and European DNA get narrower and narrower (linkage disequilibrium diminishes) with each passing generation. One can estimate how many generations have elapsed since any individual’s original Afro-European admixture took place, by the width of the stripes (by the degree of linkage disequilibrium).
A recent one-time wave of intermarriage (since the 1955-65 civil rights movement, say) would result in uniformly high linkage disequilibrium in admixed Americans. This is not observed. An ancient one-time wave of intermarriage (in the seventeenth century, say) would result in uniformly low linkage disequilibrium in admixed Americans. This is not observed either. An ongoing slow but steady Black-to-White genetic leakage across the color line for 400 years would result in a distinctive pattern of linkage disequilibrium distribution (stripes of every width occurring with equal frequency). This, in fact, is what is observed.11