Final answer:
Microsatellite DNA sequences are problematic for DNA replication enzymes due to their repetitive nature and tendency to slip during replication. They are highly variable in length across generations, making them useful markers in population genetics and ethnic ancestry analyses.
Step-by-step explanation:
The class of DNA sequences that DNA replicating enzymes have trouble copying, which changes in length through generations and is used to analyze relationships between different ethnic human populations, is microsatellite DNA. Microsatellites, also known as simple sequence repeats (SSRs) or short tandem repeats (STRs), are repetitive DNA sequences where a short motif, usually 1-6 base pairs, is repeated numerous times in a head-tail manner. These sequences are particularly prone to slippage during replication, which can result in variations in the number of repeats between generations, thus they change in length and are highly polymorphic within populations. This makes microsatellite DNA an excellent tool for genetic fingerprinting, population studies, and assessing biodiversity.