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SPEAKER 1: The
SARS-CoV-2 genome is
a single strain of
RNA with genes that
encode fewer than 30 proteins.
This is less than
0.1% of the proteins
encoded by the human genome.
The virus's genome is
made of about 30,000
building blocks called
nucleotides, which
are represented by the
letters A, U, C, and G.
The unique sequence of
nucleotides in a genome
determines the
proteins it encodes.
When the virus infects
a cell, its genome
is replicated or copied.
First, the virus makes
strands of complementary RNA
called template RNAs.
The template RNAs are used
to produce copies that match
their original virus's genome.
This genome replication
process is prone to errors.
These errors are
called mutations.
Mutations can occur at random
anywhere in the genome.
For example, in
this mutation, a U
was substituted with
an A. A nucleotide can
be substituted with a
different nucleotide,
added in the wrong
place, or left out.
When the mutated virus
infects another cell,
all the new viruses
replicated from it
will have the same mutation plus
any new mutations that occur.
Depending on the locations
and types of mutations,
they may or may not
affect the virus's ability
to spread in a population.
Viruses with mutations that
help the virus replicate
or infect cells have
a selective advantage.
These viruses usually
become more common
in a population over time.
Viruses with mutations
that make them
less effective at
replication or infection
have a selective disadvantage.
These viruses usually
become less common
in a population over time.
Mutations that have
no effect on the virus
are called neutral mutations.
Viruses with neutral
mutations replicate just
as well as viruses
without these mutations.
Tracking mutations
and viruses can
help determine where an outbreak
started and how it spread.
Understanding how virus
populations change over time
can also help scientists
develop treatments and vaccines.
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