Lecture 5 - Gene Duplication Flashcards
What is subfunctionalisation?
Where the role of a gene is split over two or more copies, and the protein made is made at two independent loci.
What is gene conversion?
Where multiple copies of a gene are advantageous when the cell needs a lot of something quickly.
What is nonfunctionalisation?
The original function of a gene is conserved within one copy, and mutations occur in the other copy and it loses function.
What is neofunctionalisation?
When one copy maintains its original function, and another is mutated to generate a new function.
Give six mechanisms of generating new genes.
- Duplication
- Exon shuffling
- Retroposition
- Mobile genetic element insertion
- Gene fusion/fission
- De novo origination
When does unequal crossing over occur?
In prophase 1 of meiosis
Where does unequal crossing over occur?
At non-homologous parts of the chromosomes
At what kind of gene is unequal crossing over likely to occur?
Where there is a repetitive sequence.
What does unequal crossing over result in?
Duplication of a part of a gene/complete gene.
What is the rate at which genes duplicate and increase to high frequency in populations?
0.01 per gene per million years.
What can happen to the second copy when a gene is duplicated?
The second copy may be free of selective pressure, and can accumulate mutations without consequences to the host.
What are two other terms for degeneration?
- Gene loss
- Pseudogenisation
What is degeneration?
One copy of a gene may accumulate mutations leading to loss of its function and potential loss of the gene.
When can we lose the ability to recognise a gene duplication?
When degeneration occurs
What is adaptive conflict?
When a single copy of a gene performs more than one function, cannot optimise one function without detrimentally affecting the other.
When is a gene said to have ‘escaped adaptive conflict’?
If gene duplication allows each gene copy to specialise to a function/each takes on a different function.
Give an example of escape from adaptive conflict.
- Antifreeze proteins in Antarctic Eelpout
- Type 3 AFP homologous to SAS (sialic acid synthase).
- AFP3s secrete d plasma proteins, bind to invading ice crystals, arrest ice growth.
- Ancestral gene fulfilled two functions, but Sas-B duplicated and moved to different chromosome.
Name the chromosomes each human globin is found on.
- Alpha: 16
- Beta: 11
- Myoglobin: 22
What are globin genes descended from?
All from a single ancestral gene.
Initial split gave rise two two lineages: myoglobin and haemoglobin.
What is exon shuffling?
The creating of new combinations of eons via intronic recombination.
What is an exon?
Part of a gene coding for proteins.
What is illegitimate recombination?
Recombination between short or non-homologous sequences.
How can exon shuffling create new combinations of exons?
By illegitimate recombination, sometimes offering new variants that give a selective advantage.
What happens in retroposition?
Processed mRNA is reverse-transcribed to form a double-stranded DNA segment. If integrated into a chromosome, the genome acquires a duplicated copy to the original gene.
What are mobile genetic elements often associated with?
Cancer
Describe how mobile genetic elements work.
- Inserts itself into an intron
- New splice sites evolve with the transposable element, and the element becomes a new exon.
How long is a mobile genetic element?
Approx 100 nucleotides
What is gene fusion?
When two adjacent genes fuse into a single gene by deletion or mutation of a stop codon.
What is gene fission?
The insertion of a stop codon followed by the insertion of a promoter region into the gene, resulting in two separate genes.
What are orphan genes?
Genes with no sequence similarity to genes in other organisms; don’t know about their ancestry.
What are orphan genes the result of?
- Fast evolutionary change relative to ancestors - no longer detect similarity.
- De novo orientation.
What is de novo gene orientation?
New coding regions emerge anew from non-coding genomic sequences.
How are de novo genes detected?
By a stretch of coding DNA encoding protein in one genome but not in the genome of a close relative.
