Which situation allows for evolution during gene duplication?
a. the original gene performs the same role as the mutated gene. b. the original gene never duplicates.
c. a mutation occurs in one copy of the original gene.
d. existing genes are copied over generations.

The first step in DNA replication is to ‘unzip’ the double helix structure of the DNA molecule. This is carried out by an enzyme called helicase which breaks the hydrogen bonds holding the complementary bases of DNA together. The separation of two single strands of DNA creates a ‘Y’ shape called the replication ‘fork’. The two separated strands will act as templates for making the new strands of DNA. One of the strands is oriented in the 5’ to 3’ direction (towards the replication fork), this is the leading strand. The other strand is oriented in the 3’ to 5’ direction (away from the replication fork), this is the lagging strand. As a result of their different orientations, the two strands are replicated differently.

For the leading strand:
A short piece of RNA called primer (produced b an enzyme called primase) comes along and binds to the end of the leading strand. The primer acts as the starting point for DNA synthesis. DNA polymerase binds to the leading strand and then ‘walks’ along it, adding new complementary nucleotide bases to the strands in the 5’ to 3’ direction. This is called continuous.  

For the lagging strand:
Numerous RNA primers are made by the primase enzyme and bind at various points along the aging strand. Chunks of DNA called Okazaki fragments are then added to the lagging strand also in the 5’ to 3’ direction. This type of replication is called discontinuous as the Okazaki fragments will need to be joined up later.  

Once all the bases are matched up, an enzyme called exonuclease strips away the primer(s). The gaps where the primer(s) were are then filed by yet more complementary nucleotides. The new strand is proofread to make sure there are no mistakes in the new DNA sequence. Finally, an enzyme called DNA ligase seals up the sequence of DNA into two continuous double strands. During the zipping up of the DNA molecule, there is a possibility that the pairing of bases get shuffled and thus cause for mutation. The result of DNA replication is two DNA molecules consisting of one new and one old chain of nucleotides. The answer is C.

Mantle convection  is the slow  creepingmotion of earth's solid silicate  mantle  caused by  convection  currents carrying  heat from the interior  to the planet's surface.[1][2]  the earth's surface  lithosphere, which rides atop the  asthenosphere  (the two components of the  upper mantle), is divided into a number of  plates  that are continuously being created and consumed at their opposite  plate boundaries. accretion occurs as mantle is added to the growing edges of a plate, associated with  seafloor spreading. this hot added material cools down by  conduction  and  convection  of heat. at the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of  subduction  usually at an  ocean trench.[3]this subducted material sinks through the earth's interior. some subducted material appears to reach the lower mantle,[4]  while in other regions, this material is impeded from sinking further, possibly due to a phase transition from  spinel  to  silicate perovskiteand  magnesiowustite, an  endothermic reaction.[5]the subducted oceanic crust triggers  volcanism, although the basic mechanisms are varied. volcanism may occur due to processes that add buoyancy to partially melted mantle causing an upward flow due to a decrease in density of the partial melt.secondary forms of convection that may result in surface volcanism are postulated to occur as a consequence of intraplate extension[6]  and  mantle plumes.[7]it is because the mantle can convect that the  tectonic plates  are able to move around the earth's surface.[8]mantle convection seems to have been much more active during the  hadean  period, resulting in gravitational sorting of heavier molten  iron, and  nickel  elements and  sulphides  in the core, and lighter  silicate minerals  in the  mantle.

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