dna and evolutionary relationship

8/8/2019 DNA and Evolutionary Relationship

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THE ROLE OF DNA IN

EVOLUTION


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DNA IN ANCESTRY

The earth today is not as it was billions ofyears ago.

However, life did exist and geneticinformation was passed down over thecenturies.

Genetic information needs to be in a formthat can be copied and transferred to thenext generation.


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Nucleic acids are the only molecules that areable to function this way.

Therefore, ALL living things have nucleic acid tostore and transfer genetic information.

One of the earliest organisms are theprokaryotes.

Through evolution and diversity we now have

eukaryotes.

However, the shape of the DNA in theseorganisms differ.


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PROKARYOTIC CELL


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EUKARYOTIC CELLS


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Prokaryotic cells include

the bacteria and archaea.

Prokaryotic cells have

plasmids, small

accessory rings of DNA.

No nucleus

Naked DNA

Animal and plant cells are

eukaryotic cells.

Eukaryotic cells have a

nucleus that controls theworkings of the cell

The nucleus is the single

greatest step in evolution

of higher animals

DNA OF EUKARYOTES AND

PROKARYOTES


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Evolution of the Eukaryotic Cell

According to the endosymbiotic theory,

eukaryotes arose from a symbiotic relationship

between various prokaryotes.

Heterotrophic bacteria became mitochondria.

Cyanobacteria became chloroplasts.

Host cell was a large prokaryote that was

evolving into a eukaryote.


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Evolution of the eukaryotic cell


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Todays eukaryotic organelles evolved bysymbiosis.

This symbiosis occured when one speciesof prokaryote was engulfed by a bigger

species prokaryote.

This bigger prokaryote was a precursor toeukaryotes.

The smaller prokaryote were not digestedin the bigger prokaryote.


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Therefore, they survived and became part of the

cell.

Their survival gave an advantage to the host

cell.

E.g.: mitochondria source of energy

chloroplast photosynthesis

Mitochondria originated from an aerobic bacteria

and chloroplast from a photosynthetic bacteria.


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Evidence for the endosymbiotic hypothesis

is the following:

Mitochondria and chloroplasts are similar to

bacteria in both size and structure.

Both organelles are bounded by a double

membrane the outer membrane may

represent the engulfing vesicle, and the innermembrane from the prokaryote.


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Mitochondria and chloroplasts each contain a limited

amount of genetic material and divide by splitting.The DNA is a circular loop like that of prokaryotes.

Most proteins of mitochondria and chloroplasts are

now produced by the host cell, but these organellesdo have their own ribosomes and do produce some

proteins. Their ribosomes resemble those of

prokaryotes.

The RNA base sequence of the ribosomes in

chloroplasts and mitochondria suggests a

prokaryotic origin.


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COMPARING DNA SEQUENCES

At least 1.7 million species of living organisms

have been discovered, and the list grows longer

every year (especially of insects in the tropical

rain forest). How are they to be classified?

Ideally, classification should be based on

homology

Homology is, shared characteristics that have

been inherited from a common ancestor.


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The more recently two species have

shared a common ancestor, the more

similar they are.

Similarities can now also be studied at the

level ofproteins and DNA


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Anatomical homology: an example

The figure shows the bones in the forelimbs ofthree mammals: human, whale, and bat

Although used for such different functions asthrowing, swimming, and flying, there is thesame basic structure.

In each case, the bone shown in color is theradius.


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Body parts are considered similar if they

have:

the same basic structure

the same relationship to other body

parts, and, as it turns out,

develop in a similar manner in the

embryo.

Various changes are adaptations.


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DNA AND PROTEIN

SEQUENCES IN ANCESTRY Because all cells use the same DNA

system, they have a common ancestry.

Mutation is a spontaneous or induced

change in the genetic material and it is

part of the evolution process.

Due to mutations, there is a great diversity

from the original DNA.


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If two species have evolved from a

common ancestor and their separation

was recent, then only a few new mutation

in each species would have taken place in

their nucleotide sequence.

SPECIES A

SPECIES A 1

SPECIES A 2


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On the other hand,

if the two specieshave been

separated for a

much longer time,

they will probablyhave more

difference in their

nucleotide

sequence.


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An organisms DNA and its proteins are

records of its heredity.

Biologist compare the nucleotide

sequence of particular genes of differentspecies to discover how related they are to

each other.

The more similar the nucleotide sequence,

the more closely related they are (close

evolutionary distance).


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The greater the evolutionary distance

between species, the more proteins (and

DNA) are different.

Differences in protein sequences and DNA

can be used to estimate time when two

species shared a common ancestor.


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COMPARE THE BASE SEQUENCES OF THESE

3 SPECIES. WHICH TWO ARE MORE CLOSELY

RELATED TO EACH OTHE

R? WH

Y?

SPECIES

BASE SEQUENCE OF A

SEGMENT OF DNARED

PANDA

G-A-G-T-A-C-C-A-T-T-A-C-G-C-

A-C

GIANT

PANDA

T-A-G-T-T-C-C-A-T-T-A-C-G-C-T-

G

RACOON

G-A-G-T-A-C-C-A-T-T-A-C-G-C-

A-T


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Answer:

The DNA sequence of the Redpanda and the racoon is the

closest match.

Therefore, the racoon and the red

panda are more closely related toeach other among the three.


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Proteins are made up of amino acid sequences.

One type of protein used in evolutionarycomparison is Cytochrome C.

Comparison of Human Cytochrome C toCytochrome C in other animals :

100 amino acids different in tuna fish

12 amino acids different in a horse8 amino acids different in a kangaroo

1 amino acid different in a monkey

Identical to chimpanzee


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Haemoglobins are sometimes usedinstead of cytochrome C in comparing

amino acid sequences.

Haemoglobins have beta chains.

The number of amino acids in the beta

chain is compared among species.


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Gorilla 1

Gibbon 2

Rhesus monkey 8

Dog 15

Horse, cow 25

Mouse 27

Gray kangaroo 38

Chicken 45

Frog 67

Lamprey 125

Sea slug (a mollusk) 127

This table shows the

difference in thenumber of amino acid

residues, in

comparison with

humans.

The human beta

chain contains 146

amino acid residues.


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Comparison Methods

There are 3 methods used to compare the DNA

sequences of different species:

DNA Sequencing

DNA Fingerprinting

DNA-DNA Hybridization

All these methods involves first isolating the

corresponding DNA segment from each species.


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DNA-DNA HYBRIDIZATION

DNA-DNA hybridization is a technique used tocompare the relationship between two speciesof organisms.

The DNA from the two species to be comparedis extracted

It is then purified and cut into short pieces (e.g.,

600-800 base pairs).

The DNA double strand is then separated byheating (92OC) into two single strands.


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The single-stranded DNA of one species isallowed to anneal with a single stranded

DNA of the other species.

The mixture is then cooled.

The more similar the DNA, the more thepieces will anneal and form hybrid DNAfragments.

Strands with a high degree of similarity willbind more firmly (meaning there will be

many complementary base-pairing).


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To assess more the degree of similarity,the DNA hybrid mixture is heated again.

Poorly matched strands separate easilyeven at low temperatures compared to

well-matched strands.

The DNA from closely related speciesshould match well.

Those from distantly related species willbe less closely matched.


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dna and evolutionary relationship

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