This is a slideshare that describe phylogenetic relationship in molecular evolution

1. EVOLUTION
Topic:: Phylogenetic relationship-Homology,Homologous
sequence of protein and DNA, Orthologous & Paralogous
MERIN TESS ZACHARIAS
1ST MSC ZOOLOGY
NIRMALA COLLEGE
MUVATTUPUZHA
ROLL NO:4861

2. CONTENT
● MOLECULAR EVOLUTION
● PHYLOGENETIC RELATIONSHIP
● MOLECULAR HOMOLOGY
● HOMOLOGOUS
● ORTHOLOGOUS
● PARALOGOUS

3. MOLECULAR EVOLUTION
● It is the area of evolutionary biology that studies evolutionary changes
at molecular level
● Molecular evolution is the process of change in the sequence
composition of cellular molecules such as DNA, RNA & Proteins across
generation.
● It includes the study of rates of sequence change ,relative importance
of adaptive and neutral changes & change in genome structure

4. ● DNA sequence comparison can show how different species
are related
● Eg:: The amino acid sequence of cytochrome c in humans and
chimpanzee is identical ,although they diverged 6 million years
ago
- Between human and rhesus monkeys,which diverged from
their common ancestor 35 million to 40 million years ago ,it
differ by only one amino acid replacement.

5. PHYLOGENETIC RELATIONSHIP
● Phylogeny means the evolutionary
history of organisms.
● Phylogenetic relationship are the
relationships that show how far back
two species shared a common
ancestor.
● Phylogenetics is important bcoz it
enriches our understanding of how
genes,genomes ,species & molecular
sequences evolve.

6. Amino acid sequences in individual proteins can be informative about
the evolution of individual gene
● In order to overcome the phylogenetic problem, now a days
we use molecular information rather than placing exclusive
reliance on morphological characters

7. ● On molecular level ,we can obtain information by comparing
sequences of nucleotides in various DNA & RNA molecules, as well
as by comparing sequences of amino acids in different Proteins.
● Molecular comparisons transcend barriers among organism whose
relationships cannot be evaluated by traditional experimental
techniques
● This close tie to the molecular Biological has transformed evolution
from a “ theoretical explanation of historical events to an observable
& continues link among life forms”

8. MOLECULAR HOMOLOGY
● HOMOLOGY is the characteristic shared by two species that is similar
because of common ancestor.
● Molecular homology -species placed in the same taxonomic category
show similarities in DNA,RNA & Proteins.
● The molecules that carry the instructions for constructing and
running the living organisms, ie DNA & RNA shows homology across
species

9. ● By comparing the differences between sequences of same protein in
different species, evolutionary biologist can determine when the two
species split off from their common ancestor & began to evolve
independently
● The more recently two species descended from a common ancestor,
the more similar their DNA sequences.
● DNA encodes instructions for every living thing on earth .This itself
is powerful evidence of common ancestry.

10. *In molecular Biology, it is mainly genes & Proteins that are
homologized.
*Evolution oriented molecular biologist working for instance in
molecular evolution or molecular phylogeny, view the concept of
molecular Homology is derived parallel to the concept of Homology in
morphological structures.
*Their focus is on how genes evolve and how they are related.
*Genes are homologous in case they are derived from an ancestral
gene.

11. Eg: Humans and
chimpanzees share a
similarity in the
sequence of amino
acid in hemoglobin.

12. Hemoglobin comparison between humans and other vertebrates

13. HOMOLOGY
● It forms the basis of organization for comparative biology
● In genetics the term ‘homolog’ is used to refer both
homologous protein and to the gene encoding it.
● As with anatomical structures ,homolog between protein or
DNA sequences is defined in terms of shared ancestry
● Two segments of DNA can have shared ancestry because of
either a speciation event( orthologs)or duplication
event(paralogs)

14. Sequence Homology
● Sequence Homology is the sequential arrangement of
bases in DNA and RNA and amino acid in case of Proteins
● Homologs are two or more sequences that descent from a
common ancestor
● They are the results of divergent evolution

15. HOMOLOGS
ORTHOLOGS
XENOLOGS
PARALOGS
RESULT OF SPECIATION
EVENT
RESULT OF GENE
DUPLICATION EVENT
RESULT OF HORIZONTAL GENE
TRANSFER

16. ORTHOLOGS
● They are sequences which are the results of speciation
event
● Similar and identical sequences in different species
● Uses::
*construction of phylogenetic tree
*comparison of evolution of genes
*Give information about classification of organisms

17. PARALOGS
● They are sequences that arose due to gene duplication
event
● Similar sequences within same species
● Two types :::
1 ] In paralog -Genes that have duplicated after a
speciation event
2 ]Out paralog-Genes that have duplicated before
speciation event

18. Paralog sequences are important
- Help in the study of Protein evolution
- Provide useful insight into the way genome
evolve.

19. ORTHOLOGS PARALOGS

20. Homology:: Orthologs & paralogs

21. GENE PHYLOGENY AS RED AND
BLUE BRANCHES WITHIN GREY
SPECIES PHYLOGENY
TOP:: Ancestral gene duplication
produces two paralogs
A speciation event produces orthologs
in the two daughter species (human &
chimpanzees)
BOTTOM :: in a separate species
(E.coli) a gene has a similar function
but has a separate evolutionary orgin
and so is analog

22. THANK U 😊