Transcript Chapt24 slides - Workforce3One

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Chapter 24 – Genome
Evolution
• Comparative Genomes
• Powerful tool for exploring evolutionary divergence
among organisms
• Footprints on the evolutionary path between different
species
• Helped to differentiate between different kingdoms
• Comparison between human and pufferfish
genome – first time for two vertebrates
• Shared a common ancestor 450 million years ago
• Some genes common were conserved and many are
unique to both
• 97% of human genome is repetitive DNA but less
than 1/6 of Fugu sequence has repetitive DNA
• Comparison between human and mouse genomes
• Humans and mice diverged 75 million years ago
• Human genome shares 99% of its homology with
mice (300 genes are unique to each)
• Comparison between human and chimpanzee
genomes
• Humans and chimpanzees diverged 35 million years
ago and show high homology
• DNA mutations: Non-synonymous changes alter
amino acid codes but synonymous do not alter them
• Single nucleotide substitutions, insertions and
deletions of DNA bases found
• Comparative Genomes
• Differences in generation time accounts for different
rates of genomic evolution
• Organisms with smaller generation time have faster
evolution
• Rate of mutation in germ line of mice and humans is
same for each generation
• Plant genes responsible for photosynthesis has not
been found in animals
• Plants, animals and fungi have 70% homology which
is responsible for replication, repair, transcription and
translation
Fig. 24.1
Fig. 24.2
• How Polyploids guides studies of genome
evolution?
• Paleopolyploids- study of ancient polyploids
• Sequence comparisons and phylogenetic tools
establish the time and pattern of polyploidy events
• Presence or absence of duplicated gene pairs provide
information about when both genome duplication and
gene loss occurred
• All copies of duplicated gene pairs might not exist
thousands or millions years after polyploidization
Fig. 24.3
With passage of time, duplicated gene pairs might/will get lost
• Synthetic polyploids provide another source for
understanding genome evolution
• Synthesized by crossing closely related plants similar
to their ancestral species and then inducing
chromosome doubling via chemicals
• Produces sterility in the plant
Fig. 24.4
Genome
downsizing has
occurred in
M.truncatula
Fig. 24.6
Elimination or
rapid loss of
genes or whole
chromosomes
over a longer
period of time
or in short span
of few
generations
•
How Polyploids guides studies of genome
evolution?
- Polyploidization leads to a change in gene expression
• Leads to methylation of cytosine
• Leads to short-term gene silencing
- Polyploidization can lead to jumping of transposon
• Transposon can move to new position in genome
giving rise to new phenotypes
•
In plants – generation of biodiversity and
adaptations
• Evolution within Genomes – by duplication
• Aneuploidy is duplication or loss of an individual
chromosome rather than entire genome
• DNA segments may be duplicated which can lead to
loss of function, gain of a novel function or have the
total function divide into two parts. Paralogues and
Orthologues
Fig. 24.8
Two midsized ape chromosomes fused to form a human chromosome –
rearrangement of chromosomes
Fig. 24.9
Conservation of synteny – Information of conservation of
genes/synteny allows researchers to locate a gene in different
species
Fig. 24.10
Gene inactivation results in pseudogenes
70% of olfactory receptor (OR) genes are inactive pseudogenes
Half of OR genes in chimpanzee and gorilla function effectively and
95% of OR genes of New World monkey and all mouse OR genes
work very well
Humans started relying on other senses reducing selection pressure
against loss of OR gene function by random mutation
Comparison of human and chimpanzee genomes show that Or genes are
becoming pseudogenes although the number is higher in humans than in
chimpanzees
Fig. 24.11
Fig. 24.12
Fig. 24.13
Fig. 24.14
Fig. 24.14.a
Fig. 24.14.b
Fig. 24.14.c
Fig. 24.14.d
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