For this purpose,
biology curriculum, textbooks, and supplementary books
were examined and 25 propositional knowledge statements,
containing all aspects of relevant topics and concepts, were
identified. Also a concept map that accommodates the
propositional statements was constructed. In the second
phase for obtaining information about students’ conceptions,
relevant literature was reviewed, semistructured interviews
were conducted with 21 students, and a multiple choice test
with free response answers was administered to 120 students.
Thus, data about students’ misunderstandings concerning
the fundamental concepts of genetics were obtained. In the
third phase, multiple choice two-tier test items directed to
determining students’ understanding of genetics concepts
were developed through item analysis and evaluation of
student responses. Consequently, the TGCT consisting of 14
items was constructed and administered to 231 secondary
school students to conduct test reliability and item analyses.
The psychometric characteristics of the test (discrimination
indices, difficulty indices, and the functionality of the distracters)
were examined by item analyses and the findings
demonstrated that the items functioned in a satisfactory way.
Cronbach’s alpha reliability coefficient of the Turkish version
of the TGCT was found to be 0.82 [26].