Question at position 22 Genetic analysis of genes related to skin color reveal that SNPs associated with light skin are the same in all human populations, even in Africa. What does this tell us about the history of light skin alleles? Persist because of genetic driftArose independently, many times across the worldThey existed before humans left AfricaHave pleiotropic effects on multiple traitsClear my selection

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BlackTom AI · Accepted Answer

To begin, let's parse the question: SNPs associated with light skin are the same across diverse populations, including African groups, which implies a certain historical pattern for these alleles.
Option 1: Persist because of genetic drift. While genetic drift can fix alleles in small, isolated populations, the global uniformity of light-skin SNPs across distant populations makes drift an unlikely overarching explanation. Drift tends to cause random frequency changes, not the repeated retention of the same variant across many large populations.
Option 2: Arose independently, many times across the world. This would predict convergent, different variants leading to light skin in separate populations. The data describing identical SNPs across populations argues against multiple independent origins, since independent origins would more likely yield distinct genetic changes with similar phenotypes, not the exact same alleles.
Option 3: They existed before humans left Africa. This interpretation aligns with the observation that light-skin alleles are shared among diverse populations, suggesting the baseline allele was present in the ancestral human population prior to modern humans dispersing out of Africa.
Option 4: Have pleiotropic effects on multiple traits. While some pigmentation genes can have pleiotropic effects, this option does not address the key observation of cross-population similarity in the same SNPs. The question’s emphasis is historical lineage rather than the functional breadth of the alleles, so this explanation does not directly account for the shared SNP pattern.
Overall, the most coherent explanation consistent with the genetic data is that the light-skin alleles existed before humans left Africa, implying an ancestral variant carried by early humans that later spread to other populations as they migrated.

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