A developer who proposes a large residential and retail project in Dorchester has agreed to purchase two additional parcels and is expanding its scope to include 424 housing units.

Dot Block LLC wants to redevelop five acres on Dorchester Avenue currently occupied by a dozen buildings. Since it originally filed a notification letter with the Boston Redevelopment Authority in March, the developer has agreed to buy two additional parcels totaling an acre at the corner of Hancock Street and also at the corner of Greenmount Street.

To satisfy lender requirements, the current plan calls for a first phase consisting of five- and six-story buildings along Dorchester Avenue and Hancock Street containing 310 residential units above 70,000 square feet of ground-floor retail space, a five-story, 450-space parking garage and 22-space parking lot for retail customers.

The second phase would consist of 64 two-bedroom apartments or condos in eight four-story buildings along Pleasant and Greenmount Streets and a five-story building containing 50 apartments or condos.

The developer is expected to submit detailed plans to the BRA following additional community meetings, according to a letter submitted to the BRA last week by MLF Consulting LLC of Newton. Dot Block LLC is an affiliate of Boston-based developer Atlas Investment Group.