Week 5 - Eukaryote transposons

Question 1

How many base pairs does the human genome contain and what proportion code for proteins?

Answer 1

• Approximately 3 billion base pairs in the human genome.
• Only around 1.1 - 1.4% code for proteins.
• Approximately half (50%) of the human genome is made up of transposable elements.
• Transposons also make up the following percentages in other eukaryotes:
  – Approx. 75% of maize genome
  – Approx. 85% of barley genome
  – Approx. 98% of iris genome

Question 2

What do all these jumping genes do, besides jump?

Answer 2

• Landing inside a gene can result in a mutation.
• Transposons can drive the evolution of genomes.
• Can also alter gene regulatory regions and phenotypes.

Question 3

Maize controlling elements

Answer 3

• Ac and Ds elements control expression of the “C gene”
- Ac: Activator – autonomous, carries a transposase gene and can therefore transpose itself.
- Ds: Dissociation – non‐autonomous, doesn’t carry a transposase gene.
• Ac encodes the transposase required to excise and move Ds to a new location, i.e. within the c gene.

Question 4

What causes the purple, yellow and spotted phenotypes in maize?

Answer 4

Purple - positive for the C gene
Yellow - negative for the C gene
Spotted - due to unstable mutations caused by a controlling element.