chapter 10 and 11

fossils

any preserved remains of a once living organism→ allows scientists to build a sequence of evolution for a particular organism

Fossil types

Petrified, mould and cast, trace, carbon film and preserved remains

petrified

turn to stone, fully dissolved minerals in water seeps through layers of sediment and hardens when evaporated

mould and cast

mould is the hard part, cast is result of mould and fills empty space of mould

trace

shows activity of an organism, sediment becomes solid rock *no water allowed

carbon film

organism dies and buried in sediment, material that makes organism breaks down and carbon remains, thin layer can show a print

preserved remains

whole organism is preserved, amber, tar or ice

amber

organism trapped in trees sticky resin and dies, more resin covers sealing insect inside

tar

organism is trapped in tar pit and dies, tar soaked into bones and stops bones from decaying

ice

organism dies in cold region, body frozen in ice which preserves organism, even hair

fossil formation

buried by sand, mud and volcanic ash or other members of species, buried rapidly or conditions not ideal for decay then decomposition is slowed

not favourable conditions for fossilisation

wet, acidic soils dissolve minerals in bone, therefore no fossil formed

favourable conditions

soils with no oxygen (peat) result in complete preservation of soft tissue and bone, alkaline soils, new minerals in soil deposit in pores of bones

stages of fossilisation

1. death and decay, 2. deposition, 3. permineralisation, 4. erosion/exposure

discovery of fossils

erosion, earth movements and excavation can expose fossils and artefacts (made by humans)

absolute dating

Polymerase chain reaction (PCR)

is used to make many copies of a section of DNA

PCR steps

Denaturing DNA to separate the strands, annealing primers to the DNA and then extension of the strands

Primers

Short sections of DNA with a base sequence that is complementary to sections on either side of the DNA that need to be copied

DNA Polymerase

Used to add nucleotides to the growing strand, enzyme needs to withstand high temp so Taq polymerase (heat loving bacterium used)

DNA ladder

Produced by running a sample with known DNA lengths through gel electrophoresis, results from known sample can be compared giving information about unknown

How to visualise DNA after gel electrophoresis

Ethidium bromide, methylene blue or DNA probes

How to find sequence of nucleotides

Sanger’s method

Sangers method

Uses dideoxyribonucleotides to stop the extension of the DNA strand, then gel electrophoresis allowing to know length and base sequence

ethical factors

autonomy, condentiality, equity and privacy need considered when gaining and using genetic information

Comparative genomics

Is the comparison of the DNA of different species, recent common ancestor will have more similarities

Endogenous retroviruses (ERV)

Viral sequences that become part of the organism’s DNA in a gamete, comparison of amount and location of ERV of different species evidence for common ancestors

Mitochondrial DNA (mtDNA)

circular DNA in mitochondria passed down from the mother, degree of mutation used to determine the closeness of the relationship between species, Higher rater of mutation, amount proportional to length of time passed

ubiquitous proteins

cytochrome C, amino acid sequence can be compared and used to infer how recently the common ancestor of two species existed

Protein sequences

proteins from same species will have same AA, therefore comparing similar proteins across species can determine relation

Bioinformatics

uses computers to describe the molecular components of a living organism.

DNA profile/ fingerprint

banding patterns of DNA fragments as a means of identification; a DNA fingerprint is unique to a particular individual

Annotation

Identification of genes in a DNA sequence

Genome

The complete set of genetic material in a cell; an organism’s complete set of DNA

Stages of PCR

Denaturing, annealing and extension

fossils

preserved traces left by organisms that lived a long time ago

How form

when parts of organism buried quickly in conditions that prevent decomposition, in soil with low oxygen

absolute dating

gives actual age, potassium-argon dating, radiocarbon dating

potassium-argon

based on decay of radioactive potassium to form calcium-40 and argon-40, for older than 100,00-200,00 years, decays at constant rate therefore proportion of potassium and argon determines age

carbon- 14

uses decay of carbon-14 to nitrogen, when organism dies carbon-14 decays, therefore ration of carbon-14 to carbon-12 used to calc age of sample, less than 60 000 years old

relative dating

tells whether one sample older or younger than other, dated before present time (BP), principle of superposition

Principle of superposition

correlation of rock strata and index fossils

stratigraphy

layers (strata) of sedimentary rock on top younger than beneath

Index fossils

Widely distributed and present for short time (known), presence in strata from different areas indicates that the rock in both areas is the same age

fossil record incomplete

The fossil record is incomplete, as fossilisation does not always occur, persistence of fossils and accessibility

Phylogenetic trees/ dendrograms

Are used to represent the evolutionary relationships between species