Everything you want to know about the neutral theory of evolution and two of the important taxonomic markers along with molecular clock hypothesis

1. Molecular Evolution
and Taxonomic
Markers

2. CONTENTS
Molecular Evolution
01
.
Modes of Molecular
Evolution
02
.
Neutral Theory of
Evolution and Molecular
Clock
03
Genetic Markers for
Taxonomic purposes
04

3. Molecular evolution is the
process of change in the
sequence composition of
cellular molecules such as
DNA, RNA, and proteins
across generations.
The field of molecular
evolution uses principles
of evolutionary biology
and population genetics to
explain patterns in these
changes.
MOLECULAR EVOLUTION

4. History of Molecular Evolution

5. Modes Of Molecular
Evolution
01
02
Substitution
type of mutation in which one
nucleotide is replaced by a
different nucleotide.
.
Insertion
type of mutation that involves
the addition of one or more
nucleotides into a segment of
DNA.
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-Evolution is caused by mutations of genes.
-Mutations spread through the population via
genetic drift and/or natural selection.

6. Modes Of Molecular
Evolution
03
04
Deletion
type of mutation that
involves the loss of one or
more nucleotides from a
segment of DNA.
.
Inversion
A chromosomal defect in which a
segment of the chromosome
breaks off and reattaches in the
reverse direction.

7. Modes Of Molecular
Evolution
03
04
Gene Duplication
.
Recombination
Genetic variations can arise
from gene variants (also called
mutations) or from a normal
process in which genetic
material is rearranged as a cell
is getting ready to divide
(known as genetic
recombination). .
New genes/proteins occur through
the gene duplication and
recombination.
type of mutation in which
one or more copies of a DNA
segment (which can be as
small as a few bases or as
large as a major
chromosomal region) is
produced.

8. Images & Contents
This neutral theory claims that the
overwhelming majority of evolutionary changes
at the molecular level are not caused by natural
selection, but due to genetic drift of mutant
alleles that are neutral. Motoo Kimura advanced
the Neutral Theory of Molecular Evolution in
1968.
Most mutations are selectively neutral at the
molecular level.
1. Most natural populations harbor high levels of
genetic variation higher than would be expected if
natural selection were the evolutionary force
primarily responsible for influencing the level of
genetic variation in populations.
.
2. Many mutations in sequences of genes do not
alter the proteins encoded by those genes. If protein
function is not altered by a mutation, the allelic
variant that results from that mutation is unlikely to
be influenced by natural selection.
Two observations underlie the theory :

9.  Random genetic drift causes major
evolutionary changes.
 Therefore, by this theory, levels of
molecular variations in genome are
strongly influenced by balance between
mutations( which causes genetic
variations) and random genetic drift (which
can eliminate the variations.
 Motoo Kimura calculated on average
sequence evolution in mammals had been
very rapid: 1 amino acid change every 1.8
years.
 Such a high mutation frequency suggest
the majority of substitutions have no
fitness effects, i.e. selectively neutral, and
are created by genetic drift.
Rate of molecular evolution is equal to the
neutral mutation rate, this gives rise to the
concept of "molecular clock”. Neutral theory is not Anti- Darwinian!

10. MOLECULAR CLOCK HYPOTHESIS
The molecular clock is a figurative term for a
technique that suggests that the mutation
rate of biomolecules with similar functional
constraints are fairly uniform during the
time period after divergence from a common
ancestor.
 Amount of genetic difference between
sequences is a function of time since
separation.
 Rate of molecular change is constant
(enough) to predict times of divergence.
 It is sometimes called a gene clock or an
evolutionary clock.
The (almost) constant rate of divergence of
the amino acid sequences of the hemoglobin

11. Genetic Markers for taxonomic purposes
.
A genetic marker is a gene or DNA sequence with a known location on a chromosome
that can be used to identify individuals or species.
Amplified
Fragment Length
Polymorphism
(AFLP)
Single-nucleotide
polymorphism(SNPs)
Restriction
Fragment Length
Polymorphism
(RFLP)
Random
Amplified
polymorphic
DNA(RAPD)
Microsatellites, or
simple sequence
repeats (SSRs)
Allozyme
Markers

12. Single-Nucleotide Polymorphism(SNPs)
40% 50%
60%
80%
01
02
03
If you are reading a news story where it says, for
example, scientists find the genetic contributors to
diabetes or some other condition or trait, you're
probably reading about SNPS. An SNP is a one-letter
place where your genome varies from another
genome sequence.
SNPs (single nucleotide polymorphism)A
single nucleotide polymorphism (abbreviated
SNP, pronounced snip) is a genomic variant
at a single base position in the DNA.
Thanks to the Human Genome Project, we
have found that these single-letter changes in
our genetic code are placed all across our
genomes. We can see that the patterns vary
between people and even between
populations.
Suppose we want to identify genetic contributors to a
common complex disease like diabetes. In that case,
we can group thousands of people who have diabetes
and compare their SNP patterns to thousands of people
who do not have diabetes. With enough people in our
study, we can use the SNPs as markers to see that
some regions of the genome appear to be the same in
people who have diabetes, and that tells us where we
should look in more detail for a genetic cause.

13. -RAPD is a polymerase chain reaction (PCR) based method.
-It is a molecular marker that helps to identify genetic variations.
-For RAPD several arbitrary, short primers (8-12 nucleotides) are used which can bind randomly in
genomic locations.
-No knowledge of DNA sequence is required. Hence a popular method.
-Identical 10-mer primer will or will not amplify a segment of DNA, depending on positions that are
complementary to the primer sequence.
In order for PCR to occur:
1) the primers must anneal in a particular orientation (such that they point towards each other) and,
2) they must anneal within a reasonable distance of one another.
Random Amplified Polymorphic DNA(RAPD)

14. Random Amplified Polymorphic DNA(RAPD)
PRINCIPLE:
 The principle is that a single, short oligonucleotide primer,
which binds to many loci, amplifies random sequences from a
complex DNA template.
 This means that the amplified fragment generated by PCR
depends on the length and size of both the primer and the
target genome
.These amplified products (of up to 3.0 kb) are usually separated
on agarose gels (1.5-2.0%) and visualized by ethidium bromide
staining.
 Nucleotide variation between different sets of template DNA
will result in the presence or absence of bands because of
changes in the priming sites.
Recently, sequence characterized amplified regions (SCARS)
analysis of RAPD polymorphisms showed that one cause of
RAPD polymorphisms is chromosomal rearrangements such as
insertions/deletions.
The drawback? is- random primers can amplify many sequences.
Hence, the bands obtained are closely spaced and difficult to
analyze.