Question

why during DNA replication antron are formed

Answer 1

Hey there,

I think that you got the wording wrong. Maybe you're actually referring to introns rather than 'antron'. First, introns are not formed during DNA replication but rather during synthesis of mRNA during transcription in eukaryotes. Actually, in eukaryotes, exact copies of the complementary base pairs of the DNA template are not formed in the mRNA, meaning that the mRNA molecule doesn't align exactly with the stretch of DNA encoding it. There are large gaps which are formed in the mRNA. These are called introns (they are the non-coding part of the gene being transcribed). The resulting mRNA is actually known as the pre-mRNA, and before translation, these introns are removed by a process known as RNA splicing which gives rise to the mRNA which is used for translation.

Hope it helps.
You can also take a look at this tutorial:
RNA splicing
URL: http://bcs.whfreeman.com/thelifewire/content/chp14/1402001.html

P.S: Please note that introns are not formed in bacteria. This event happens in only eukaryotes.