Complex sentence: In Brazil there has been extensive admixture between Europeans, Amerindians and Africans, resulting in no clear differences in skin color and relatively weak associations between self-reported race and African ancestry.
Split into simpler sentences: In Brazil there has been extensive admixture between Europeans, Amerindians and Africans. As a result, skin color differences within the population are not gradual, and there's relatively weak associations between self-reported race and African ancestry.