Medical Genetics Ultraviolet radiation causes pyrimidine dimers These can block DNA replication Also, dimers interfere with base pairing between the tWo dNA polymeres U.V. light also generates free adicals which create other kinds of genetic damageMedical Genetics Ultraviolet Radiation causes pyrimidine dimers. These can block DNA replication. Also, dimers interfere with base pairing between the two DNA polymeres. U.V. light also generates free￾radicals, which create other kinds of genetic damage