Answer:
Before cell division must occur, the chromosomes must replicate themselves. Sister chromatids are the two initially identical copies.
The mRNA made from the section of DNA coding for the protein (the gene) exits the nucleus through a nuclear pore after getting modified. It can get modified by getting a poly-A tail and a methylated cap, along with removing the interfering sequences (introns).
Answer:
oxygen: it was the result of biological activities. There were such stable continental shelf environments, which were rare in the Archean, developed after 2.5 billion years ago, facilitating the growth of photosynthetic organisms and thus oxygen production.