comparative genomics
comparing the genomes of different species to find out how closely related they are
genome - complete set of DNA in each cell of an organism
more similar the genomes of 2 species are, the more closely related the 2 species are
because common features of 2 species are likely to be encoded within the DNA conserved evolutionarily between them
shows diversity of gene composition of different evolutionary lineages
ERVS
endogenous retroviruses are viral sequences that has become part of an organisms genome, genetic information stored as RNA
copies its RNA onto DNA through reverse transcription, then inserts the DNA into one of the chromosomes of a host cell
only becomes endogenous if inserted into a cell whose chromosomes will be inherited by the next generation
ERV will be present at the same location in chromosomes of all cells of all subsequent generations
more ERVs possessed by different species in exactly the same location in their genomes, the more closely related they are
mtDNA
small circular molecules, 5-10 per mitochondrion
37 genes, 24: tRNA, 13: enzymes for cellular respiration
- more mitochondrial DNA than nuclear DNA present, easier to find and extract
- inherited only from the mother, easier to trace direct lineages
- higher mutation rate than nuclear DNA
- mtDNA of species slowly diverges from mtDNA of ancestor as time passes, no. of mutations is roughly proportional to amount of time passed since evolution
- more diversity of mtDNA, less closely related 2 species are
ubiquitous proteins
proteins that are present in and carry out the same basic function in every organism
assign each amino acid a single letter and arrange them in sequence, comparisons can be made between these sequences
number of differences in the sequence is observed
- less differences, more similaries
- more differences, more time since evolution from common ancestor
cytochrome c: essential step in the production of cellular energy
bioinformatics
- science of collecting, analysing, understanding complex biological data using computational techniques to analyse data
- combines computer science, statistics, math and engineering to analyse bio data
- uses computer software to store and analyse bio data rather than phyiscal taxonomy or physiological observations
- genes and other biological features in DNA need to be identified through genome annotation, made possible by start and stop codons
- compare genes of different species, more similar genes, more closely related they are
comparative anatomy
comparing structural features of different species to see how closely related they are
embryology
comparing the anatomical structures during embryo development of different species
different species that share similar anatomical structures during early development as an embryo are more closely related
provides evidence of a possible common ancestor
organisms may have features in the embryo that are not found in adults
eg gill slits on the necks of vertebrate embryos
homologous structures
sturctures that show high degree of strucutral similarities but perform different functions in different species
a possible common ancestor would have also had the same structure, common ancestor possibly exists
bones dont need to be same length or width, they are best adapted to the species environment based on the selection pressures acting on them
vestigial structures
structures that have a function in some species, but are reduced in size and appear to have no function in other species
there is no selection pressure to maintain them, reduced in size to waste less energy
more similar structures, more closely related, evidence that there could possibly be a common ancestor
define fossil
any preserved trace of an organism that lived in the past
conditions for fossil formation
- quick burial of material so that there is little exposure to the atmosphere
- microorganisms absent
- presence of hard body parts
- long period of stability
how are fossils excavated
- excavation sites where surface fossil fragments were found or evidence of human occupation like caves
- excavation site surveyed and marked out into sections
small samples taken and sieved to ensure small fossil fragments are not overlooked
artefacts
objects deliberately made by humans
absolute dating
gives the actual age of the specimen in years
potassium argon dating process
- potassium-40 decays into argon-40 and calcium-40, this process has a half life of 1.25 billion years
- as rock ages, proportion of K decreases and Ar increases
amount of radiation produced from sample measured, - - - ratio of K to Ar in sample calculated, actual age of rock then calculated
Potassium argon problems
- not all rock types suitable, only those with K-40
- fossil must be same age as rock
- date rocks 200 000+ years old due to large half life
carbon-14 dating process
- when an organism dies, it stops intaking carbon, carbon-12 remains stable, but carbon-14 decays at a fixed rate
- radiation measured, ratio of C-12 to C-14 measured, actual age calculated
- half life of 5730 years
carbon dating problems
- need 3g organic material (100mg accelerated mass spectrometry radiocarbon dating)
- levels of atmospheric carbon varies with time
- up to 60 000 years, or C-14 to small to be measured accurately
relative dating
determine whether one sample is younger or older than another sample
stratigraphy
study of layers or strata
principle of superposition
layers of rock on top are younger than layers of rock below them
top rock layer fossils are younger than fossils found in layers below them
- distortions occur in the earths crust due to movement of tectonic plates
- buried by animals or early humans sometime after the deposition of sediment
correlation of rock strata
matching layers of rocks from different areas, assume fossils in the same strata are the same age
index fossil definition
fossils of organisms that were widely distributed on earth and present on earth for a limited period of time
- define boundaries in the geological time scale, used in correlation of rock strata
how to date with index fossils
- presence of index fossils in different rock layers can be used to correlate the ages of those rock layers
- because it can be inferred that the rock layer was formed during the time period when that species existed
- if found with other fossils age can be correlated, because they have a known age range
