A nonresident individual who is married and whose spouse has income from independent sources must declare the joint income of himself and his spouse from sources within and without Mississippi and claim as a personal exemption that proportion of the authorized personal and additional exemptions which the total net income from Mississippi sources bears to the total net income of both spouses from all sources. If both spouses have income from sources within Mississippi and wish to file separate returns, their combined personal and additional exemptions shall be that proration of the exemption which their combined net income from Mississippi sources is of their total combined net income from all sources. The amount of the personal and additional exemptions so computed may be divided between them in any manner they choose.
In the case of married individuals where one (1) spouse is a resident and the other is a nonresident, the personal exemption of the resident individual shall be prorated on the same basis as if both were nonresidents having net income from within and without the State of Mississippi.
For the purpose of this subsection, the term "net income" means gross income less business expenses incurred in the taxpayer's regular trade or business and computed in accordance with the provisions of the Mississippi Income Tax Law.
Miss. Code § 27-7-21