Blood pressure forces plasma minus its macromolecules (e.g., proteins) from the glomerular capillaries into the Bowman's capsule, which is continuous with the proximal convoluted tubule.
Genetic drift is changes in allele frequencies of a gene pool due to chance or random events. This can occur in large or small populations. Genetic drift causes gene pools of two isolated populations to become dissimilar as some alleles are lost and other are fixed.
