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20 Cards in this Set

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How many human genes have a directly equvalent orthologue in mice?

- approximately 80%

What causes the biggest difference between gene content of different vertebrate genomes?

- changes in the number of members of genes within gene families




e.g. olfactory receptors - 396 in human, 1035 in mouse

How do new genes arise?

- reverse transcr. mRNA (generate retrogenes)




- exon shuffling - exons from 1 gene become inserted into or fused with another gene




- de novo - mutation of non-coding DNA




- Gene duplication

What is Gene duplication

- most new genes and new members of gene family arise through gene duplication




- every gene is believed to undergo a duplication event once every 100 mln years

How does gene duplication occur?

- Replication slippage




- unequal crossing over between repetitive sequences




- unequal crossing over between


duplicated genes




- whole genome duplications

What is replication slippage?

What is unequal crossing over between repetitive sequences?

- May occur where gene is flanked by two copies of a repetitive sequence (e.g. Alu),

- May occur where gene is flanked by two copies of a repetitive sequence (e.g. Alu),





What is unequal crossing over between duplicated genes?

- may occur where there is a cluster of two or more related genes (during meiosis)

- may occur where there is a cluster of two or more related genes (during meiosis)





Give an example of a whole genome duplication:

- Xenopus tropicalis - diploid genome




- Xenopus laevis - tetraploid genome




- may have undergone one or two rounds of gene duplication about 500 mln years ago

What is the fate of duplicated genes?

- nonfunctionalization - 1 copy becomes inactivated through mutation (pseudogene)




- neofunctionalization - one copy acquires new function




- subfunctionalization - one copy acquires a subdivision of function

Give an example of neufunctionalization:

- antifreeze glycoprotein gene in Antarctic fish encodes a glycoprotein with 41 copies of the motif Thr-Ala-Ala, evolved from a duplicate of the trypsinogen gene

Neofunctionalization - scheme

Give an example of subfinctionalisation

- if gene is expressed in several tissues, each duplicate may become expressed in a subset of the tissue that the parent gene was expressed in


- most vertebrates: single aromatase gene expressed in brain and ovary


- fish - duplicate aromatase genes, one expressed in brain one expressed in ovary

How did the hypothetical scheme for evolution of duplicated aromatase genes in fish?

- The original gene had one sequence controlling expression in brain and another controlling expression in brain




- in fish the ovary mutated one sequence and the brain - the other

What is an example of gene family generated by gene duplication?

- Haemoglobin - tetramer


- different isoforms are used in different stages of development

Evolution in the globin family:

When do pseudogenes originate?

- inactivating mutation occur in a newly duplicated genes




- inactivating mutations occurn in an existing gene that has become surplus to requirement

How many pseudogenes are there in humans?

- 3230 known; 425 are from olfactory receptors

Where do processed pseudogenes and retrogenes arise from?

- reverse transcription of mRNA molecules


- either become inactive processed pseudogene


- or potentially active retrogene

What are the differences between processed pseudogenes and pseudogenes>

- processed are derived from mRNA -no introns, no promoter, polyA tail;




- processed are distant from active related genes, normal genes may be in clusters with active genes




- processed are flanked by direct repeats