public class Person
{
    public int Id { get; set; }
    public Gender Gender { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

switch (person.Gender)
{
    case Gender.Male:
        if (IsMale(person.FirstName))
        {
            //Isvalid
        }
        break;
    case Gender.Female:
        if (IsFemale(person.FirstName))
        {
            //Isvalid
        }
        break;
}

var genderFuncs = new Dictionary<Gender, Func<string, bool>>
                {
                    {Gender.Male , (x) => IsMale(x)},
                    {Gender.Female , (x) => IsFemale(x)}
                };

public static bool IsMale(string name)
{
    //check...
    return true;
}
public static bool IsFemale(string name)
{
    //check...
    if (name == "Farzad")
    {
        return false;    
    }
    return true;
}

var dummyPerson = new List<Person>
                {
                    new Person
                        {Id = 1, Gender = Gender.Male, FirstName = "Mohammad", LastName = "Saheb"},
                    new Person
                        {Id = 2, Gender = Gender.Female, FirstName = "Farzad", LastName = "Mojidi"}
                };

foreach (var person in dummyPerson)
{
    bool isValid = genderFuncs[person.Gender].Invoke(person.FirstName);          
}

var query = context.Students.AsQueryable();
  if (searchByName)
  {
      query= query.FindStudentsByName(name);
  }
  if (orderByAge)
  {
      query = query.OrderByAge();
  }
  if (paging)
  {
     query =  query.SkipAndTake(skip, take);
  }
  return query.ToList();

var searchTypeFuncs = new Dictionary<SearchType, Func<IQueryable<Student>, string, IQueryable<Student>>>
                    {
                        {SearchType.FirstName, (x, y) => x.FindStudentsByName(y)},
                        {SearchType.LastName, (x, y) => x.FindStudentsByLastName(y)}
                    };

public static IList<Student> SearchStudents(IQueryable<Student> students, SearchType type, string keyword)
{
    var result = searchTypeFuncs[type].Invoke(students, keyword);
    return result.ToList();
}