1. Higher Biology
Unit 1:
1.7 Evolution

2. Learning Intentions
To be able to describe the process of gene transfer in different organisms

3. Success Criteria
I can explain how genes are transferred in eukaryotic organisms
I can explain how genes are transferred in prokaryotic organisms
I can explain how genes are transferred in viruses

4. Evolution
Evolution is the process of gradual change in the characteristics of a population of organisms that occurs over successive generations
Evolution occurs as a result of variations in the population’s genome
These variations take the form of changes in the frequency of certain genetic sequences (how often alleles appear)

5. Inheritance
Genetic sequences of DNA are passed on from parent to child
This is known as vertical transfer
This can occur by either asexual or sexual reproduction

6. Sexual reproduction
During sexual reproduction two organisms with different genomes produce offspring with a different genome to either parent
This increases variety within a population
Vertical inheritance in this manner can be shown using a family tree in humans

7. A family tree allows us to see inherited characteristics passing down from one generation to the next (vertically).

8. Asexual Reproduction
During asexual reproduction a parent produces a genetically identical copy of itself (a clone)
No variation will result in successive generations unless mutations occur

9. Vertical gene transfer
Transfer of genes from parent to offspring is relatively safe
The genes passed from parent to child have allowed the parents to survive and reproduce so must offer some benefits

10. Horizontal Transfer
In prokaryotes genetic material can transfer horizontally from one cell to another
This means that genetic information can be exchanged within the population and not just passed from parent to offspring

11. Rapid evolutionary change is believed to have occured in prokaryotes due to horizontal gene transfer (HGT) occurring
Prokaryotes were able to acquire beneficial genes from other cells rather than waiting for the gene to evolve over time
With HGT there is no guarantee that the gene received will be beneficial

12. The need for HGT decreased as multicellular organisms reached higher levels of complexity
Vertical inheritance allowed for the formation of distinct lineages with their own sets of genes

13. MRSA HGT still occurs in prokaryotes
Certain bacteria exchange plasmids that carry genes for resistance to antibiotics form one bacteria species to another
This has resulted in strains of bacteria resistant to several antibiotics
One of these is methicillin-resistant Staphylococcus Aureus (MRSA)

15. HGT between species
Some prokaryotes are able to transfer genes into eukaryotes
The soil bacterium Agrobacterium tumefaciens infects wounded plant cells with a plasmid which integrates a sequence of its DNA into the genome of the plant
A harmless version of this plasmid can be used in genetic engineering to improve crop plants

16. HGT in viruses
Some viruses transfer their DNA horizontally into the genome of a host organism
This allows viruses to reproduce within host cells but also lie dormant
Examples include herpes, and HIV

17. Success Criteria
I can explain how genes are transferred in eukaryotic organisms
I can explain how genes are transferred in prokaryotic organisms
I can explain how genes are transferred in viruses