Evolution of mouse globin superfamily

Evolution at the Molecular Level
Evolution of genomes
 Review of various types and effects of
 How larger genomes evolve through
duplication and divergence
 Molecular archeology based on gene
duplication, diversification, and selection
globin gene family: an example of
molecular evolution
Speculations on how the first cell
The first step to life must have been a
replicator molecule
The original replicator may have been RNA
More complex cells and multicellular
organisms appeared > 2 billion years after
cellular evolution
Earliest cells
evolved into three
kingdoms of living
Archaea and
bacteria now
contain no introns
 Introns late
Fig. 21.3
Basic body plans of some Burgess shale organisms
Many species resulting from metazoan explosion
have disappeared
Fig. 21.4
Evolution of humans
35 mya – primates
6 mya – humans diverged from chimpanzees
Fig. 21.5
Evolution of Humans
Human and chimpanzee genomes 99%
Karyotypes almost same
No significant difference in gene function
Divergence may be due to a few thousand
isolated genetic changes not yet identified
Probably regulatory sequences
DNA alterations form the basis of
genomic evolution
Mutations arise in several ways
 Replacement of individual nucleotides
 Deletions / Insertions: 1bp to several Mb
 Single base substitutions
 Missense mutations: replace one amino acid codon with
 Nonsense mutations: replace amino acid codon with stop
 Splice site mutations: create or remove exon-intron
 Frameshift mutations: alter the ORF due to base
 Dynamic mutations: changes in the length of tandem repeat
Effect of mutations on population
Neutral mutations are unaffected by agents
of selection
Deleterious mutations will disappear from a
population by selection against the allele
Rare mutations increase fitness
Genomes grow in size through
repeated duplications
 Some
duplications result from
 Other
duplications arise from
unequal crossing over
Genetic drift and mutations can turn
duplications into pseudogenes
Diversification of a duplicated gene followed
by selection can produce a new gene
Genome size
duplication of
exons, genes,
gene families
and entire
Fig. 21.10
Basic structure of a gene
Fig. 21.11
Genes may elongate by duplication of exons to
generate tandem exons that determine tandem
functional domains
e.g., antibody molecule
Fig. 21.12a
Exon shuffling may give rise to new genes
e.g., tissue plasminogen activator (TPA)
Fig. 21.12b
Duplications of entire genes can
create multigene families
Fig. 21.13a
Unequal crossing over can expand and
contract gene numbers in multigene families
Fig. 21.13b
Fig. 21.14a
Intergenic gene conversion can increase
variation among members of a multigene
One gene is changed, the other is not
Concerted evolution can lead to gene
Fig. 21.15
Unequal crossing over
Gene conversion
Evolution of gene superfamilies
Large set of genes divisible into smaller sets,
or families
Genes in each family more closely rated to
each other than to other members of the
Arise by duplication and divergence
Evolution of globin superfamily
Fig. 21.16
Organisation of globin genes
Fig. 21.16
Evolution of mouse globin superfamily
Fig. 21.16
Evolution of mouse globin superfamily
Fig. 21.16