How was it spelt!

My g grandfather was born 1846 in Ireland !  however, my dna is from  Co Mayo/ Sligo according to Ancestry   -   could be the origin of my maiden name.  My maiden name was spelt GRACHAN   - has been recorded as GRAHON GREHAN GRAGHAN GREGHAN GREAGHAN  - but finding the marriage of his parents John and Mary !!!  is proving impossible 

One dna match has a William Grehan born at Ballycastle 1855  his father was Pat.

My g grandfather Martin came to Australia as a 10 year old with his mother and older brother Michael b 1837 (according to a court case) However, because of the numerous spelling variations  I have not been able to find his arrival into Australia This is all I know   He died in 1885 so a lot of family history does not exist.    Looking at records the surname could have been spelt Gaughan Greahan in Ireland  

I will continue reading the messages posted here and your articles.    One day my wall will crumble.     I have seen other surnames in persons posts that are found in the family trees of my dna matches