public class MyAccountViewModel
{
    public string Username { get; set; }
    public string LastName { get; set; }
    public string MiddleInitial { get; set; }
    public string State { get; set; }
    public string ZIP { get; set; }
    public string Telephone1 { get; set; }
    public string Telephone2 { get; set; }
    public string Email { get; set; }
    public string PreferredLanguage { get; set; }
    public int DateOfBirthDay { get; set; }
    public int DateOfBirthMonth { get; set; }
    public string NewPassword { get; set; }
    public string ConfirmNewPassword { get; set; }
    public List<QuestionAnswerPairModel> SecurityQuestionAnswers { get; set; }
    public List<SelectListItem> AllowedQuestions { get; set; }
    public List<SelectListItem> PreferredLanguageList
    {
        get
        {
            return new List<SelectListItem>
            {
                new SelectListItem { Text = "English", Value = "en", Selected = PreferredLanguage == "en"},
                new SelectListItem { Text = "Español", Value = "es", Selected = PreferredLanguage == "es"},
            };
        }
    }

    public UserRegistration ToUserRegistration()
    {
        return new UserRegistration
        {
            Username = Username,
            FirstName = FirstName,
            MiddleInitial = MiddleInitial,
            LastName = LastName,
            AddressLine1 = Address1,
            AddressLine2 = Address2,
            City = City,
            State = State,
            Zip = ZIP,
            Telephone1 = Telephone1,
            Telephone2 = Telephone2,
            Email = Email,
            PreferredLanguage = PreferredLanguage,
            DateOfBirthDate = DateOfBirthDay,
            DateOfBirthMonth = DateOfBirthMonth
        };
    }
}

public class QuestionAnswerPairModel
{
    public int QuestionId { get; set; }
    public string Answer { get; set; }

    public QuestionAnswerPair ToQuestionAnswerPair()
    {
        return new QuestionAnswerPair
        {
            QuestionId = QuestionId,
            Answer = Answer,
            HasChanged = Answer != "Type your answer"
        };
    }
}

[HttpPost]
public PartialViewResult UpdateMyAccount(MyAccountViewModel myAccountViewModel)
{
    //the myAccountViewModel property has null set for all properties
}

$.ajax({
    url: '@Url.Action("UpdateMyAccount", "MyAccount", new {area = ""})',
    type: 'post', // type: 'POST'
    //datatype: "json",
    contentType: "application/json; charset=utf-8", // contentType: "application/json"
    data: getMyAccount(), // data: JSON.stringify(getMyAccount()) and data: JSON.stringify({'myAccountViewModel': getMyAccount()}) and data: JSON.stringify({myAccountViewModel: getMyAccount()})
    success: function() {
        makeAjaxCall(accountInfo);
    }
});

function getMyAccount() {
            return {
                Username: $('#Username').val(),
                FirstName: $('#FirstName').val(),
                LastName: $('#LastName').val(),
                MiddleInitial: $('#MiddleInitial').val(),
                Address1: $('#Address1').val(),
                Address2: $('#Address2').val(),
                City: $('#City').val(),
                State: $('#State').val(),
                ZIP: $('#ZIP').val(),
                Telephone1: $('#Telephone1').val(),
                Telephone2: $('#Telephone2').val(),
                Email: $('#Email').val(),
                PreferredLanguage: $('#PreferredLanguage').val(),
                DateOfBirthDay: $('#DateOfBirthDay').val(),
                DateOfBirthMonth: $('#DateOfBirthMonth').val(),
                NewPassword: $('#NewPassword').val(),
                ConfirmNewPassword: $('#ConfirmNewPassword').val(),
                SecurityQuestionAnswers: [
                    {
                        QuestionId: $('#originalQuestionId0').val(),
                        Answer: $('#answerId0').val(),
                    },
                    {
                        QuestionId: $('#originalQuestionId1').val(),
                        Answer: $('#answerId1').val(),
                    },
                    {
                        QuestionId: $('#originalQuestionId2').val(),
                        Answer: $('#answerId2').val(),
                    }
                ]
            };
        }

{"myAccountViewModel":{"SecurityQuestionAnswers":[{},{},{}]}}