Answer:
When helicase mutations occur, problems in DNA replication are found. The helicases are proteins that open the 2 strands of DNA to initiate the duplication, they are responsible for breaking the hydrogen bonds between the two DNA chains, thus separating the chains, also they have the function of repairing DNA mutations, if there is mutation in the gene that encodes them, various functions will be absent in the cell.
Answer:
C. At least five mass-extinction events have occurred during the last 500 million years.
Explanation:
- The history of mass extinct is related to the five mass extinctions that are caused over by the 350 million years n which many species have disappeared in there short geologic time.
- A massive extinction is caused in the Permian Triassic extinction event i.e about 250 mn years ago which on an estimate has killed 90% of the species.
- The Cretaceous–Paleogene extinction event that occurred over 66 million years ago is known to have wiped out the dinosaurs and many other species.
Lasting genetic similarities make the two bears biological sister species, more closely related to one another than to any others. ... But Ursus maritimus has also evolved to match its polar environment, growing a longer snout than brown bears' and larger, paddle-like paws, both of which aid polar bears in hunting seals.
C. The Bering Land Bridge once connected what would be Russia and North America but the the movement of these continents separated the land bridge
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