As expected, the Mariners have activated outfielder Franklin Gutierrez from the 60-day disabled list. Gutierrez is in the line-up tonight, starting in center field and batting sixth.

To make room on the 25-man roster, the Mariners have placed Michael Morse on the 15-day disabled list. Morse is eligible to come off on July 6 since it’s retroactive to June 21

To make room on the 40-man roster, outfielder Eric Thames was designated for assignment.

Gutierrez took early batting practice and regular batting practice and didn’t suffer an injury pregame.

“It’s been a long time,” he said. “I’ve been having a long rehab. I’ve had some issues with my legs. It hasn’t been easy for me. I’m feeling much better. I’m feeling more normal now. That’s the only thing that matters right now. I’m going to try to do whatever I can to help the team.”

Gutierrez initially went on the disabled list with a strained hamstring, but this has been a season long issue where’s felt discomfort in his hips, knees and legs in general.

Recently, doctors figured out that Gutierrez has a genetic disorder that basically causes inflammation and arthritic pain in his joints and other parts of his body.

“I started taking some medicine, and it’s working now,’ Gutierrez said. “It took about three or four weeks to start feeling better. I didn’t know what I had and they didn’t know either. They found out that it caused all these things. As soon as I started the medicine, I started feeling better and better and better.”

Gutierrez wasn’t sure of the exact name of the condition and Mariners medical staff chose not to comment on specifics other than it was a disorder causing inflammation in the joints.

“They finally figured out what was going on,” Gutierrez said. “It wasn’t their fault, because they’re doing a really good job on me, doing everything I ask them to do. I guess we got to the time where they found out what it is, and I’m feeling much better. It was affecting my joints, my eye was getting inflammation. So many people didn’t know about this, and we didn’t need to talk about it until now. Obviously, I don’t want to make a big deal about this, but it’s what’s been happening. I’m feeling much better now. I’m taking the medication, it’s working.”

Gutierrez has missed 53 games this season. It was the third straight season, he’s missed more than 50 games.