Lecture 6 - Horizontal Gene Transfer and Transposable Elements Flashcards
What is horizontal gene transfer?
The movement of genetic material from one organism to another by other means than parent to offspring.
Give an example of how horizontal gene transfer has been detected.
In HMGCoA reductase gene in Archaean taxon, found to be acquired from bacterial lineage.
Where does yeast mitochondrial Heat Shock Protein 70 (hsp70) originate from?
S. cervisiae hsp70 more closely related to proteobacterial proteins than to other forms of yeast cells.
In what organisms does horizontal gene transfer normally occur?
Prokaryotes
Give an example of horizontal gene transfer in animals.
The coffee berry borer beetle has protein similar to mannanase, which breaks down a polysaccharide in coffee beans.
Mannanase has bacteiral origin.
Donor lineage is likely to be beetle’s own gut bacteria.
What kind of genes are transferred horizontally in prokaryotes?
- Pathogenicity factors
- Antibiotic resistance genes
What is a transposable genetic element?
A genetic element that can move from one position on a chromosome to another position on the same or a different chromosome, many laving a copy behind.
Who discovered transposable elements?
Barbara McClintock, 1940s/50s
What were transposable elements originally thought to be?
Junk DNA
What is the aleurone layer of maize?
The coloured protein layer, which is triploid
How are genes inherited in maize?
Two sets of alleles inherited from maternal line, and one from paternal line.
What is special about chromosome 9 of maize?
Readily breaks and is correlated with colour change.
What are the roles of the following alleles in maize?
a) C’
b) C
a) C’ = dominant allele, prevents colour from being exposed to aleurone layer.
b) C = recessive allele, leads to colour development in layer.
What are the roles of the following alleles in maize?
a) Bz
b) bz
a) Bz = dominant allele, produces purple colour.
b) bz = recessive allele, produces dark brown colour.
What is the role of the Ds allele in maize?
It is the genetic location where chromosome breakage occurs.
What kind of kernel would you expect with the presence of a C’ allele in maize?
Why might you not?
- A colourless kernel
- Due to breakage in some F1s, C’ is absent, resulting in pigmentation.
What causes partial colour in maize?
- An unstable phenotype
- Movement of Ds into C’ site, disrupting some parts of the kernel.
What are both Ac and Ds shown to be?
Class II transposons
What activates Ds?
Ac
Why is Ds activated by Ac?
It is a transposon with a mutation in its transposes gene, and is a non-autonomous element (needs something else present)
What are Class 1 transposable elements?
Retrotransposons; those that go via an RNA intermedia.
What are class 2 transposable elements?
DNA transposons.
What percentage of the human genome is made up of transposable elements?
44.4%
What is the c-value paradox?
- Where c-value denotes the haploid DNA content
- Refers to the fact that observed complexity correlates very poorly with the haploid quantity of nuclear DNA.
How many base pairs in the human genome?
3 billion
How many mega-bases in the human genome?
3,200
How many genes in the human genome?
26,000
What percentage of the human genome is made up of protein-coding genes?
30%
What percentage of the protein-coding DNA in humans is
a) Exons?
b) Introns?
c) Repetitive DNA?
a) Exons = 2%
b) Introns = 28%
c) Repetitive DNA = 45%
True or false:
Number of proteins is less than the number of genes.
FALSE.
Number of proteins is greater than the number of genes.
What can complexity be generated by?
Alternative splicing.
What percentage of human genes can produce multiple different mRNA variants?
90%
Give the size of the microsporidia genome.
2.9Mb
In the microsporidia genome, how many of the following are there?
a) Chromosomes
b) Genes
a) 11 chromosomes
b) 1998 genes
What is the size of the E coli genome?
5Mb
What percentage of the microsporidia genome is
a) Protein-coding DNA?
b) Introns?
a) PCD = 86%
b) Introns = 0.02%
Give the size of the Trichomonas vaginalis genome.
160Mb
How many of the following are there within the Trichomonas vaginalis genome?
a) Chromsomes?
b) Genes?
a) 6 chromosomes
b) 60,000 genes.
What does Trichomonas vaginalis not have that is present in the genome of humans?
A mitochondrial genome.
What percentage of the T vaginalis genome is
a) Protein-coding genes?
b) Repetitive DNA?
a) PCG = 34%
b) RD = 66%
What organism has the genome with the largest number of predicted proteins?
Trichonomas vaginalis
