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Genome Evolution (Signatures of evolution in the genome (Orphan genes:…
Genome Evolution
Signatures of evolution in the genome
About 5% of the genome is conserved across all mammals
Methods of genome evolution
The location of gene can change
The total gene number and genome size (in base pairs) can change
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How does this happen?
Duplication
Transferred between species
Homolog: Gene or sequence that is similar
Ortholog: Gene similar in different species due to common ancestor
Paralog: Gene similar due to a duplication event
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Orphan genes: Genes that "come out of nowhere"
No orthologs (similar genes in closely related species) exist
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Consists of 10-30% on average of a genome
Somehow come from non-functional DNA
Possible outcomes of duplication
Both copies retain their original function, but expression differs
One copy stops functioning (coding for proteins)
One copy accumulates enough base pair substitutions to gain a new function
Both copies retain their original function
The genome
All the DNA in an organism
Prokaryotes have much smaller genomes than eukaryotes
As genome size increases, the percentage of it that consists of functional coding genes decreases
Genome size typically has very little to do with complexity
Large genomes may be constrained by selection (DNA may be energetically costly)
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Genome size varies more than gene number
Point mutations in DNA
Substitution: When an entire population has the same point mutation (called fixation)
Synonymous (or silent): Substitution does not effect the coded amino acid (no fitness effect)
Fate of the allele (and trait) determined by genetic drift
Non-synonymous: Substitution changes what amino acid lis coded for
Fate of the allele (and trait) determined by selection