Fredo - In 2018, an analysis of DNA from the entire genome indicated that domesticated dogs 
entered North America from Siberia for 4,500 years and were then isolated for the next 9,000 years. 
After contact with Europeans, these lineages were replaced by Eurasian dogs and their local descendants. 
The pre-contact dogs exhibited a unique genetic signature that is now almost gone.[2] In 2020, 
the sequencing of ancient dog genomes indicates that in 
two Mexican breeds the Chihuahua retains 4% and the Xoloitzcuintli 3% pre-colonial ancestry.[3]