Ms Waddell studied social and political thought in Brighton
Police investigating the murder of a woman whose body was found strangled after a fire at her flat in Brighton have arrested a 42-year-old man.
The body of Andrea Waddell, 29, who had a masters degree and worked as a prostitute, was found just before midnight on Thursday by firefighters.
The man in custody, from Brighton, was held on Saturday night, police said.
Ms Waddell's family have revealed she underwent gender reassignment surgery after moving to Brighton in 2004.
In a statement, they said she had originally been born Alexander John.
Ms Waddell studied for a masters degree in social and political thought at the University of Sussex, after graduating in philosophy at Durham.
During his time at Durham, Mr Waddell began hormone treatment, and ended the three-year course as Andrea Joanna.
Ms Waddell, who grew up in Reading, Berkshire, was said by police to be very close to her parents Sonia and Robin and her brother Nick.
"Our beloved Andrea has been through so much," they said in their statement.
They revealed she was diagnosed at 14 with several spinal curvature and developed fibromyalgia, a permanent condition of chronic pain.
"After moving to Brighton she developed acute ulcerative colitis which nearly killed her, but she was saved by having her colon removed, resulting in an ileostomy [that was reversed a year later]," they said.
The body of Ms Waddell was found as firefighters made the scene safe
"Andrea continued to live in Brighton, often incapacitated by pain but fiercely independent.
"We know she is now finally free of this pain and at peace."
Police have renewed their appeal for information about Ms Waddell's death, particularly from other members of Brighton's sex industry.
Det Ch Insp Adam Hibbert, who is leading the murder inquiry, said on Saturday Ms Waddell was sociable and well known, but was not known to drink or take drugs.
It is not known how the fire at the flat in Upper Lewes Road started or whether it was started deliberately. It was contained in Ms Waddell's bedroom.
She was last seen alive some time on Thursday. Her car has been towed away for examination.
Mr Hibbert said she was "discreet" about her work, but was known sometimes to take clients home with her.
He did not disclose what was used to strangle Ms Waddell or whether her body was set on fire.