The groups says Dobson left the company following a restructure of research responsibilities on the emerging market and Asian equity desks.
She took over as lead manager of the fund in September 2007 after its former manager, Jules Mort, stepped down to focus on institutional mandates.
Julian Thompson, the head of global emerging markets, has taken over the management of the Latin American vehicle with Mort still acting as deputy manager.
Threadneedle says Thompson was closely involved with the Latin American mandate and there is a high degree of overlap between this and the Global Emerging Markets portfolio.
Analysis: Resilience in Latin America