Answer and explanation:
If no bands were visible on the gel for some samples I'd interpret this result as in a very possible pippeting error that did not allow the sample to load correctly. Pippeting error can be caused by many factors, for example, if our chosen pipet is broken or dirty this can cause amount of liquid reduction after the transfer process.
The concept that Marsiglia and Kulis are referring to from the statement mentioned in the question is a term called intersectionality.
Intersectionality is a concept that is generally defined as <em>a framework that acknowledges how an individual is impacted by various systems of power – and his or her position in each system, when combined would create a different experience in how an individual would be treated by the society at large. </em>
For example, an individual who identifies as Black, is female, has an upper middle class income, is heterosexual would navigate life differently from someone who is White, male, has a lower class income, and is homosexual.