"United States Census, 1850," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MCDY-GYZ : 12 April 2016), John G Brown in household of William Brown, Roane county, part of, Roane, Tennessee, United States; citing family 412, NARA microfilm publication M432 (Washington, D.C.: National Archives and Records Administration, n.d.).
Source: S-1010523963 Repository: #R-1349419655 1880 United States Federal Census Ancestry.com and The Church of Jesus Christ of Latter-day Saints Publication: Ancestry.com Operations Inc
Repository: R-1349419655 Ancestry.com
Source: S-1010531249 Repository: #R-1349419655 1850 United States Federal Census Ancestry.com Publication: Ancestry.com Operations, Inc.
It may be possible to confirm family relationships with John by comparing test results with other carriers of his ancestors' Y-chromosome or mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree: