The game begins with the classic appearance of the original Space Invaders. However, this soon gives way to Charles Darwin's theory of evolution, setting the tone for the remainder of the game. At the start of the game, the ship features the general controls of being able to move left and right and shoot. However, by progressing through the game and earning 'genes', the game goes through evolution, introducing new aspects such as being able to move the ship in all directions. As the game progresses, evolutions unlock various features such as new weapon types, an increased life limit, as well as unlockable music and bonus stages. During the game, players can shoot down UFOs to release DNA which, when collected, increases the effectiveness of their selected weapon. The DNA will scatter if the player loses a life. Players can chain enemy kills to increase their score, and also perform 'Nagoya Attacks', in which the player can pass through certain enemy fire the moment it is launched.
Source: Wikipedia, "Space Invaders Infinity Gene", available under the CC-BY-SA License.