What does the genome tell us about being human? Flashcards
What is comparative genomics used for?
- To discover what is in common and what is different
- Things in common are called ‘conserved’ and may encode biology in common between species
- Things that are different may encode organism specific biology
- So by comparing genomes you learn a little about which bits of the genome do what
How do you compare individual genome sequences?
- By lining up next to each other and marking each point where sequences are the same
- This is called ‘aligning’
Why would we compare the genome of species to others?
By comparing genomes between individuals we can find out where difference occurs Differences such as: - Disease - Characteristics of an individual - Evolutionary history
What could we learn about an organism if we compare its genome with others?
- What sort of genes they have
- How differences between species arise
- Relationships between species
What animals are the closest relatives of humans?
Chimps and bonobo
What is a neanderthal?
- Probably the closest relatives of modern humans.
- Lived 130,000 - 30,000 years ago in Europe and Asia
- Unsure of why they died
- Good remains for DNA extraction
What did they get when trying to sequence the neanderthal DNA?
- 4 billion nucleotides
- Identified and discount modern contamination
- Gathered sequence from 3 individuals
- Enough sequence to compare with modern human genome sequences from around the world
- Identified bits of DNA that differ between neanderthals and us
What did they find out when they sequenced the neanderthal DNA?
- Some of us carry neanderthal DNA
- Modern humans from Europe and Asia carry neanderthal
- Those from Africa show no signs of these alleles
- The most explanation for this is that where modern humans met neanderthals, they interbred.
How much neanderthal DNA do non-Africans hold?
2-4%
What do the neanderthal variants in our DNA do?
That it adds variation to our genome that may be related to our phenotype
e. g. GG at a particular locus - more likely to get sunburnt as a child (arose in neanderthals)
- Variation gained from neanderthals affect the phenotype of humans.
Were only homo sapians and neanderthals sequenced?
No, a finger bone whose mitochondrial DNA doesn’t match neanderthal or modern human DNA
- The genome from this species of human was sequenced from a tooth found in the same cave in 2010
- This is a denisovan
Do human genomes contain Denisovan DNA?
Denisovan variation is also found in the human genome, where it makes up 4-6% of the genomes of present-day melanesians (east asia)
What hybrid human species was found? What does this tell us?
A Neanderthal Denisovan hybrid
- Evidence for inbreeding in ancient human species
What does studying the genomes of other human species tell us?
By studying the genomes of homo sapiens and our ancient extinct relatives we can build and understanding of our evolutionary history
Why is it hard to make a genome sequence of our closer relatives (ancient human species)?
- DNA from dead things can remain in the environment
- DNA degrades and is masked by more modern DNA
- DNA bases are also modified as they degrade, sometimes changing the sequence
It can be extracted and identified in very special circumstances
