Horizontal Gene Transfer

Question 1

horizontal gene transfer

Answer 1

also lateral gene transfer

• transfer of DNA between unrelated or sexually divergent species
• transposons, genes, segments of genome etc.
• among bacteria (conjugation, transduction, transformation)
• between prokaryotes and single cell eukaryotes
• prokaryote endosymbiont and euk host
• occasionally btw eukaryotes

Question 2

HGT between eukaryotes

Answer 2

rare
-some transposons in drosophila and related insects
- parasitic plants and hosts
- symbionts and hosts
- occasionally other examples
Occurs by:
-vector organisms, like viruses and parasites
- between parasitic plants and host plants
- between endosymbiont and host
-between bacteria and eukaryotic cell

Question 3

How HGT involving eukaryotes occurs

Answer 3

Occurs by:

• vector organisms, like viruses and parasites
• between parasitic plants and host plants
• between endosymbiont and host
• between bacteria and eukaryotic cell

Question 4

how HGT is detected

Answer 4

• Genes: incongruence between gene tree and species tree
• • this could also be ILS, insufficient resolution of gene used, or hybridization between the species
• – need to eliminate these before can conclude is HGT
• more convincing if donor species is identified and if there is a physical relationship between them (parasite etc.)

Question 5

how gene tree can show HGT

Answer 5

mitochondria gene from parasite to host plant example

• pseudogenes copy is derived from parasite not normal vertical transfer
• incongruence between gene tree and species tree

Question 6

How can Horizontally transferred genes become functional

Answer 6

• successful incorporation into genome
• incorporation at position that allows for expression
• inserted at position that does not disrupt a critical gene
• gain regulatory elements for expression (unless already in HGT gene)

many HGT do not go through all these steps== pseudogene

Question 7

crown galls

Answer 7

Agrobacterium tumefaciens
way to transform genes into plants
- T1 plasmid – TDNA– inserts into plant chromosomal DNA
-crown gall = massive cell proliferation analogous to cancer but NOT detrimental to health

Question 8

risks of HGT

Answer 8

bioengineered plants may exchange genes with natural species

- transfer of antibiotic resistance genes between bacteria: makes more bacterial infections resistant to antibiotics

Question 9

how to identify HGT on genome wide scale with transcriptome approaches?

Answer 9

• analyze transcriptome and find overlaps but doesnt characterize full extent of HGT
• sequence full genome to get full picture

sequence transcriptome of different genomes to provide a database for transcript sequences
- sequencing will show other genes and gene fragments that were not seen before in comparative analysis between species