Sometimes, chemical damage to dna can occur just before dna replication begins, not giving the repair system enough time to correct the error before the dna is duplicated. this gives rise to mutation. if the cytosine in the sequence tcat is deaminated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of dna replication?

1)ttat
2)tuat
3)tgat
4)taat

layer 3 is younger than layer 6.

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.