Question

How is that cDNA stands in contrast to what the central dogma of molecular biology say?

Answer 1

The central dogma of molecular biology says that genetic
information is transferred only in direction DNA -> RNA -> protein,
and information is never transferred in the opposite direction.
However, the dogma was stated in 1958 and now it has several
exceptions, like cDNA. This kind of DNA is synthesized by the enzyme
(reverse transcriptase) using RNA template (cDNA becomes complementary
to the RNA). Thus, genetic information flows in direction RNA -> DNA,
what does not correspond with the central dogma. However, synthesis of
cDNA is a rare event in molecular biology.