MBB 267 Week 4: Barnes 5

Question 1

How often does transposition happen?

Answer 1

Not that often – cellular defence mechanisms come into play to reduce transposition
1-One transposition in hundreds of cell generations
2-transposition events will only be fixed if they occur in a germline genome!
3-over evolutionary time, transopsotion is important in shaping genomes

Question 2

What can transposon cause to the genome?

Answer 2

Can cause exon shuffling or duplication of whole genome

Question 3

What is exon shuffling?

Answer 3

When the exons are shuffled in the gene

Question 4

How does exon shuffling happen?

Answer 4

2 ways:

• Due to crossing over between transposons in different parts of the genome
• -Exons of different genes that are both flanked by the same transposon are swapped over when there is recombination in the transposon sequence
• Due to “mistakes” in transposition
• -An exon in-between two DNA transposons might be excised from the genome and inserted at a new location (moved by another transposon movement)
• -A LINE transposon might use the polyA signal of a neighbouring gene instead of its own, thus adding the exon onto its normal transcript

Question 5

How does gene duplication happen?

Answer 5

Three main mechanisms:
1-Replication slippage
2-Unequal crossing over
3-Retrotransposition of an mRNA

Question 6

What are solitary genes?

Answer 6

Genes with that are only present once in the genome. Gene duplication is common in multicellular eukaryotes.

Question 7

What are orthologous and paralogous genes?

Answer 7

two different classes of homologues:

• Orthologues: evolved by speciation. These genes have been evolving separately since the divergence of the two species.
• Paralogues: evolved by duplication. These genes have been evolving separately since the gene duplication event.

Question 8

What happens to tandemly repeated (duplicated) genes?

Answer 8

eg, rRNA gene has been amplified and now forms a tandem array (350 copes in human genome)

• In this case, all the copies are conserved because very high amounts of RNA need to be transcribed
• Non-transcribed spacer sequences are in-between can be quite divergent but genes are relatively well conserved

Question 9

What are the possible fates of a duplicated gene?

Answer 9

3 possibilities:

• Degradation: too many mutations -> becomes a pseudogene = a gene with no function
• Neofunctionilisation: new copy gains a jew fucnion
• Subfunctionilisaiotn: Each copy is specialised.

Question 10

What are pseudogenes?

Answer 10

Has accumulated mutations that prevent the gene from functioning: frameshifts and point mutations that generate premature stop codons, faulty splicing, etc

Question 11

What are processed pseudogenes?

Answer 11

Generated by reverse transcription of a functional mRNA and insertion of the cDNA into the genome, by LINE proteins. These inserted sequences don’t have the proper processing signals, so generally are not functional.

Question 12

What is an example of gene duplication?

Answer 12

the globin gene family

• Human haemoglobin
• -Transports oxygen in vertebrate blood
• -2 α-family + 2 β-family chains
• -The members of the globin gene families expressed varies throughout prenatal development

Question 13

What is an example of subfunctionalization?

Answer 13

the vertebrate globin genes
-The vertebrate globin gene family contains a number of members, generated by gene duplication events, that have evolved to have slightly different properties