 This work led to the first successful sequence-based analysis of the genomes of single cancer cells from tumors by Wigler's then-graduate student Nick Navin, and subsequently, tumor cells in circulation by Wigler's collaborator Jim Hicks.In the early 2000s, Wigler, Jonathan Sebat and Lakshmi Muthuswamy began copy number analysis of healthy individuals, leading to the discovery of a new source of genetic variability, copy number variations or CNVs.The abundance of CNVs in the human genome is a major source of individual variation.