When two comparisons groups within an experiment are identical except for one variable the experiment is called

Controlled experiment

Explanation:

A controlled experiment is a type of experimentation that is done under controlled conditions. The procedure entails changing or manipulating one (sometimes more than one) variable or factor at a time, but keeping everything else the same between the groups.

This is done to ensure that the factor or variable they are testing is what elicits any changes in the subject. One group is always kept in normal or standard conditions, to serve as a base line to compare to.  

tsd is temerature dependent sex determination.

tsd: it is a type of environmental sex determination in which the temperature experienced during embryonic/ larval development (ambient temperature for development) determine the sex of the offspring.

crocodile displays the tsd where the ambient temperature of the developing egg determines the individual's sex. for example in the american alligator's eggs, incubation at 33 ºc produces mostly males, while incubation at 30 ºc produces mostly females. so if the american alligator's egg will get the ambient temperature (33 degree celcius)during embryonic development from egg, the offspring will be male and same for the female sex determination.