Evidence for evolutions

Comparative genomics definition

Comparative genomics is where the genome sequences of different species are compared.

Endogenous retroviruses (ERV's)

Examples of non-functional DNA that are remnants of ancient retroviral infections, which have become part of an organisms genome.

ERV's make up 8% of the human genome and match the chimpanzee ERV's on 16 instances, supporting the theory that they share a common ancestor.

Protein sequence comparisons

By comparing the type and sequence of AA in similar proteins from different species, the degree of similarity can be determined.

Animals of the same species have identical AA sequences, while different species have variations in their sequences or order.

Ubiquitous proteins

A protein that appears to be in all species, that are essential for all organisms to live.

Cytochrome C

An ubiquitous proetin that has changed very little over millions of years.

Human cytochrome C has 104 AA, with 37 found in the same positions across all species studied.

Suggesting all cytochrome C proteins evolved from an ancestral form in a mircorbe that lived around 2,000 mya.

Mitochondrial DNA consists of:

small circular molecules, with 5-10 per mitochondrion and 500-1000 copies per cell, making it easier to find and extract than nuclear DNA .

What does mtDNA contain?

Contains 37 genes for tRNA used in protein synthesis and 13 enzymes needed for cellular respiration. In humans, mtDNA has about 16,500 base pairs.

Why is mtDNA used for comparative biochemistry?

mtDNA has a higher rate of mutation than nuclear DNA. Hence, has been slowly diverging from the mtDNA of our original female ancestor. The amount of mutation is proportional to the amount of time that has passed.

Examples of what comparison of mtDNA has found?

Migration patterns: most Europeans descend from Ice Age hunter-gatherers, not Middle Eastern farmers.

Modern humans and neanderthals shared a common ancestors around 600,000 years ago.

Bioinformatics definition?

Bioinformatics is the use of computers to describe the molecular components of living things.

Annotation

How a DNA sequence is compared to another by using computers to find start and stop codons.

Fossil definition

A fossil is any preserved trace left by an organism that lived a long time ago.

Can be bones, shells, teeth, footprnts, burrows, faeces or impressions.

How does wet, acidic effect fossilisation?

Soils the minerals in the bone, dissolving them and no fossilisation occurs.

Effect of no oxygen on fossilisation

Complete preservation of the soft tissues and bones of the animal may occur. E.g. peat.

Effect of alkaline soil on fossilisation

Produces the best fossils because the minerals in bones aren't dissolved.

Effect of minerals like lime or iron oxide on fossilisation

Lime or iron oxide fill the pores of the bone, replacing the organic materal. This process turns the bone into rock while preserving its structural details.

Location of fossils

Human ancestors are often found where water was in the past. This is because the organism can be buried rapidly preventing decomposition.

Limestone which makes up many caves contains calcium carbonate that can build up around dead organisms. Sometimes, the cave collapses burrying remains.

3 Issues with the fossil record

Incomplete fossilisation: conditions for fossilisation are a chance occurence.

Not found: only a small proportion of fossils that exist have actually been discovered.

Difficult to date: dating fossil materail can be problematic.

4 conidtions required for fossilisation

quick burial of the material

presence of hard body parts

absence of decay organisms

a long period of stability

Absoulte dating definition

Quantifying the age of the fossil

Potassium-argon dating definition

Potassium-argon dating technique is based on the decay of radioactive potassium to form calcium and argon.

How does potassium-argon dating work?

- A type of radioactive decay

- potassium-40 has 21 neutrons and is radioactive

- overtime it slowly decays into calcium-40 and argon-40

- we measure how much potassium-40 and argon-40 is in a rock

- as time passes, the amount of potassium-40 goes down, while the amount of argon-40 goes up

Radioactive decay

The breakdown of isotopes. They give off small particles and radiotion at a specific rate.

Isotopes

Atoms of the same element that have the same number of protons but a different number of neutrons.

Potassium characteristics

Made up of a mixture of 2 different isotopes. All potassium atoms have 19 protons, but potassium-40 has 21 neutrons.

What is potassium-40 half-life?

1.25 billion years. Therefore works on rocks that are more than 100,000-200,000 years old.

Carbon-14 dating

This method is based on the decay of the radioactive isotope of carbon, carbon-14 and nitrogen-14.

How is carbon-14 made and how is it present in organisms?

Carbon-14 is made in the upper atmosphere when cosmic ray hit nitrogen. This carbon-14 mixes with CO2 in the air.

It is present in organisms due to the intake of CO2 by plants via photosynthesis.

What is carbon-14's half-life?

5730 years. The max age to date is 60,000 years.

How is carbon-14 dating done?

Scientists measure how much carbon-14 is left and compare it to carbon-12 (a stable form of carbon that doesn't change). This helps them figure out how long its been since the organism died.

Relative dating definition

Putting fossils in order from oldest to youngest.

Stratigraphy

the study of rock layers and the sequence of events they reflect

Principle of superposition

A principle of stratigraphy. Assumes that layers of sedimentary rock at the top are younger than those beneath them.

Must be applied carefully as shifts in the Earth's crust occurs and fossils may be buried by animals or humans which can affect its accuracy.

Index fossils

Widely distributed across the Earth and only present on the Earth for only a limited period. Therefore, they can be used as an indicator of time when matching layers of rock from different areas by studying the fossils they contain.

Fossilised pollen grains

Are a type of index fossil but can be used to indentify the amount and type of vegetation at the time and can also indicate climate conditions.

Pros of Potassium-argon dating

- high accuracy for old materials.

K-40 decays into argon-40 with a half-life of 1.25 billion years. Therefore, it is ideal for dating very old rocks.

- Doesnt require organic material

This is useful when dating anient volcanic layers associated with fossils.

Cons of carbon-14 dating

- Limited time range, after 60,000 years more carbon-14 is gone, so the method become useless for older fossils.

- atmospheric carbon-14 levels vary. Natural fluctuations in carbon levels occur due to things like fossil fuel burning.

Pros of Stratigraphy

- simple and cost effective

Can be done by just looking at the order of sediment layers and building a basic timeline.

- Can be done for sedimentary rock

Cons of stratigraphy

- no actual dates

only a sequence of time can be made

- assumes that the layers are undisturbed

- should be used with other dating techniques

Pros of dendrochronology

- Very accurate dating

- Allows understanding of the past climate

- cross dating with other trees

Cons of dendrochronology

- Only works on trees that grow with distinct rings

- Well preserved wood is required

- Human activity can affect growth of rings