Cassette stand, reaction unit, and genetic testing apparatus

A reaction unit used in a genetic testing apparatus, the reaction unit comprising:

• a plurality of test tube units, each test tube unit constituting a lane and including a plurality of test tubes;
• and
• a cassette stand on which the plurality of test tube units is installable, the cassette stand including an internal space, an upper surface provided, for each lane, with a plurality of circular openings into which the plurality of test tubes of the lane are insertable and with a ventilation opening extending along the plurality of test tubes of the lane, and an exhaust fan installed in or connected to a lateral surface of the cassette stand and configured to exhaust gas from the internal space,
• wherein, when the plurality of test tube units is installed on the cassette stand with the plurality of test tubes inserted into the circular openings, the ventilation opening for each lane communicates a space above the plurality of test tubes of the lane with the internal space, and the exhaust fan sets the internal space to a negative pressure and generates, in each lane, a downward stream of gas from above the plurality of test tubes of the lane toward the ventilation opening of the lane.