A Labrador retriever breeder needs to determine if three male pups who were born to Sadie, his black...

A Labrador retriever breeder needs to determine if three male pups who were born to Sadie, his black Labrador retriever, are the offspring of Sam, a yellow Labrador retriever from another breeder. Which process could the breeder use to determine if Sam is the father of the pups?
PCR analysis
STR analysis
mtDNA analysis
Y-chromosome analysis