Posted Yesterday, 08:19
Keep in mind that this will depend on the strength of the hand as well. While there is a style known as MAFIA (MAjors FIrst Always), this is not very standard nor very popular. When holding a hand with game forcing values almost everyone will respond in their longest suit, or bid four-card suits up the line. So it's always possible to respond 1♦ when holding 5+♦ and 4♠ when also holding sufficient strength.
When responding to 1♣ from partner, there are a few basic styles:
1. What's known as Walsh Style is popular, especially in the US among players who use 2/1 GF (even though this is not really tied to the core of 2/1, it was popularised by many of the same books/players). In this style, you never respond 1♦ when holding a four-card major unless you have game-forcing values. So you would bypass a longer diamond suit to bid a four-card major on a weaker hand. Since opener knows that 1♣-Pass-1♦ will not normally contain a major suit, he will normally bypass the majors to rebid 1NT/2NT on a balanced hand (concealing his major suit holding). If responder has the relatively rare 5+♦ 4-card major game force hand, he can reverse into his major at second turn.
2. There's a variant of Walsh called invitational Walsh which basically works the same way except that you bid 1♦ with 5+♦ and a four-card major and game invitational values (or more). So you only bypass a longer diamond suit with less than ten points or so.
3. Modern players have noticed that the 1♦ response to 1♣ is extremely low frequency in Walsh, so many of them have shifted to Transfer Walsh, where the 1♦ response shows hearts and the 1♥ response shows spades. This gives you an extra step in the (very common) major-showing responses which some use to show a weak notrump (allowing 1NT rebid to be the big notrump) and others use to show 3-card support (allowing 1NT and 2M to deny holding three trumps).
4. Whether to rebid 1♠ after 1m-Pass-1♥ is a somewhat separate issue; everyone plays that responder could easily be 4-4 in the majors on this start but some people feel that the advantages of the 1♠ rebid guaranteeing 5+minor and the 1NT rebid immediately confirming a balanced hand are enough to compensate for missing some 4-4 spade fits when responder doesn't have enough points to invite game.
5. There are still some people (like Elianna and myself) who prefer to bid our suits up the line, but I think this is less popular among experts these days than choosing one of the methods above.
I'll add that in response to your 2nd question, I don't think anyone is bypassing a four-card major as responder to 1m in order to bid 1NT. Obviously you could find some very weird system or some expert trying to "turn the hands" so that he will always declare the notrump doing this, but it's definitely not a common or popular approach.
Adam W. Meyerson
a.k.a. Appeal Without Merit