NESA Biology Cell Replication

Helicase unwinds the double helix and separates the strands.
Polymerase adds nucleotides to the new strand.

The weak nature of hydrogen bonds makes it easy for helicase to separate strands.
Complementary base pairing allows DNA polymerase to be guided by the template strand.

Mutations occur when DNA polymerase makes an error by inserting, removing or adding an incorrect nucleotide. Substitution reactions involve A, T, C or G being swapped for a different nucleotide, and result in point mutations. Because of the way that codons work, these mutations will only affect one amino acid. Additions or deletions cause frameshift mutations, where all codons after the mutation will be affected.

Helicase unzips the DNA molecule by breaking the weak hydrogen bonds between the two complementary strands.
This creates a replication fork region so that bases are exposed.
DNA polymerase uses each original strand as a template to produce a copy of the DNA molecule, and adds complementary nucleotides to the exposed bases.
DNA polymerase also proofreads the newly synthesised strand.

Main steps:

The two strands of the DNA molecule separate. Each strand serves as a template for the synthesis of a new strand, and nucleotides are added to the new strand by DNA polymerase. Gaps are filled, and one old and one new strand combine to form a new double helix.

Nucleotide pairing: Each DNA strand consists of nucleotides, and the new strand is synthesized by adding nucleotides that are complementary to the existing strand, where adenine pairs with thymine and guanine pairs with cytosine.

Hydrogen bonds: Complementary strands are joined by hydrogen bonds, which are weak bonds. This allows for the separation of the different strands making up the molecule.

Allopatric speciation is the process by which a new species arises due to geographic isolation.

A geographic barrier subdivides an ancestral population into subpopulations, which prevents individuals from migrating between the two subpopulations. Therefore, the barrier blocks gene flow between subpopulations, meaning gene flow cannot counteract any genetic differences that evolve between them.

The environment on either side of the barrier are different. Natural selection favours different traits on either side of the barrier, which generates genetic differences between subpopulations.

Furthermore, mutation generates new alleles through a random process, meaning unique mutations and alleles will occur in each subpopulation, which also contributes to genetic differences between subpopulations.