15. Evidence for evolution + 16. fossil evidence for evolution Flashcards
What are the types of comparative studies in biochemistry?
Mitochondrial DNA
Protein Sequences
DNA
What does it mean if species share a greater portion of their DNA?
they are more closely related
What are endogenous retroviruses?
a viral sequence that has become a part of an organisms genome
retrovirus RNA enters cell and is copied into DNA –> reverse transcription –> DNA then inserted into host cell chromosome
only endogenous if it inserts into gamete cell (all subsequent generations have a copy of the virus in their cell
comprise about 8% human genome
What is mitochondria?
cell organelles where aerobic respiration occurs to release energy for cell use
What is mtDNA?
DNA in the form of small circuar molecules (5-10 in each mitochondrian)
- 37 genes
- 24 contain code for making tRNA
13 code for cell respirations reactions
rare diseases caused by mutations in mtDNA
higher rate of mutation –> slowly diverges from ancestral copies, amount of mutation is proportional to the amount of time that has passed
What is easier to extract, mtDNA or nuclear DNA and why?
mtDNA due to the fact that most cells contain large numbers of mitochondria
Why does mtDNA only come from the mother?
sperm destroys the mitochondria after entering a cell
what does it mean if the mtDNA is very similar?
two individuals are closely related, but if not similar their last common maternal ancestor lived a long time ago
What is DNA?
Deoxyribonucleic acid- very large molecule made of two strands of nucleotides that are joined by bonds between the nucleotide bases. The two strands are twisted into a double helix
found in the nucleus and mitochondria of cells
what is nDNA?
Nuclear DNA- DNA found in the nucleus of the cells
what is mtDNA?
mitochondrial DNA- DNA found in the mitochondria
What is RNA?
Ribonucleic acid - large molecule composed of a single strand of nucleotides
what is mRNA?
RNA molecule that carries the code for protein synthesis from the DNA in the nucleus to the ribosomes where the protein is made
what is tRNA?
Transfer RNA- a small RNA molecule that transfers the correct amino acid to the ribosome for inclusion in the protein molecule being made
what are ubiquitous proteins?
in all species, perform basic and essential tasks, independent of organism’s specific function or environment
what is Cytochrome C?
- performs essential step in production of cellular energy
- changes very little over evolution
- 37 amino acids in the same place in every sequenced molecule –> proteins have descended from an ancestral molecule found in primitive microbe more than 2000 million years ago
- sequences from different species are aligned and compared
what is annotation?
identification of genes and other biological features in a DNA sequence
- a computerised process, made possible by the fact that genes have recognisable start and stop codons
what are comparative studies in anatomy?
embryology
homologous organs
vestigial organs
what does embryology do?
provides evidence for evolutionary change over time by comparing the early stages in the development of organisms
how is embryology done?
by comparing embryos of different species during a pregnancy
the longer the species is similar in development, the more closely related they are
how can you tell vertebrae are related through embryology?
many vertebrae have embryonic gill pouches and arches, as well as absence of paired appendages and all have a tail (embryonic reptiles, birds and mammals) which show their common ancestor in fish millions of years ago
what are homologous organs?
possess a similar internal structure but different external appearance or function
They are likely to have a common ancestor
what are vestigial organs?
structures of a reduced size that appear to have no function, but long ago in the evolutionary timeline had a function that has diminished due to changed environment
what are examples of vestigial organs?
- nicitating membrane present in corner of each eye
- external ear muscles
- wisdom teeth erupt abnormally
- appendix
- coccyx
- erectopilli muscles
how can geographical distribution be used to provide evidence for evolution?
- the more similar structures are whilst being found in very different places shows a common ancestor
what are fossils?
any preserved trace by an organism from a previous time period, including footprints, burrows, teeth, faeces, bones, impressions of organisms, or footprints
should the organism be buried quickly or slowly to become a fossil?
quickly to prevent the decay by micro-organisms
What type of soil is best for creating fossils?
soils lacking oxygen as it may completely preserve the soft tissues and bones of the animals
- alkaline soils produce the best because the minerals of the bone don’t dissolve
what type of soil is bad for creating fossils?
wet acidic soild as they dissolve the minerals of the bone
how does a fossil become petrified?
when new minerals, often lime or iron oxide, are deposited into the pores of the bone, replacing the organic matter that makes up about 35% of the weight of the bone
where are the best fossils formed geographically?
areas of sedimentary or volcanic rock
where are human fossils often found?
at the edges of ancient lakes and river systems, in caves or volcanic areas
Lakes and rivers deposit sediments during flooding or slow water flow
many caves are in limestone which deposit calcium carbonate (prevents decay and deposits around dead organisms
why is it better to die in water?
remains are more likely to be buried by sediment and less likely to be destroyed by scavengers or erosion
low energy environments with little movements are preferable for burial- remains less likely to be destroyed by mechanical processes
is it better to have course or fine sediment?
fine as eluding oxygen and slowing bacterial decay enables soft tissues to be preserved
what are artefacts?
objects deliberately made by humans
what are the best conditions for fossil formation?
- quick burial of material
- presence of hard body parts
- absence of decay organisms
- long period of stability to leave organism undisturbed
what are limitations to the fossil record?
- right conditions of fossils rarely met
- only very small proportion have been discovered - some buried too deep, inaccessible locations, destroyed by human activity
- dating of fossil material can be problematic
- unusual to find a fossil of a whole organism, or the whole skeleton
- controversy between interpretations of fossil reconstruction
What is fossil dating?
- the determination of the age of fossilised material, which is crucial in determining the sequence of changes that resulted in the evolution of modern day humans
what is absolute dating?
- provides the actual age of the specimen in years
what is Potassium-Argon dating?
- based on the decay of radioactive potassium to form calcium-40 and argon-40
- decay takes place at an extremely slow but contant rate
- determining the amounts of potassium-40 and argon-40 in a sample enables the age of the rock to be calculated
limitations to potasium- argon dating?
not all rock types are suitable for this method (must have suitable rock of the same gage of the fossil - usually only volcanic) can only date rocks older than 100 000- 200 000 years
What is carbon-14 dating?
- based on the decay of radioactive isotope of carbon-14 to nitrogen
how does carbon 14 dating work?
- 1:1 ratio of c14 to c12 in the atmosphere –> c14 becomes a part of the animal’s tissues due to its presence in all organic material, which animals consume for food
- with death, an organism’s intake of c14 halts, but the c14 decays at a fixed rate
- measuring the amount of radiation liberated by a sample, the ratio of C14 to C12 can be estimated –> can calculate the age of the sample
what is the half-life of c14?
5370 years
what are the limitations to c-14?
-requires at least 3 grams of material, can only be used in organic substances (not rock or some artefacts)
- can’t be used to date back more than 60 000 years
c-14 values in the atmosphere fluctuate somewhat
What is AMS dating?
Accelerator Mass Spectrometry radiocarbon dating
- more refined method of radiocarbon dating
what are the advantages of AMS dating?
- used to date a sample as small as 100 micrograms
how does AMS dating work?
it breaks a sample into its constituent atoms so the number of atoms of each isotope of carbon can be counted
what are the limitations to AMS dating?
it is expensive
what does each ring on a tree represent?
- one year of growth, with rings differing in width according to how favourable the growing season was
- rings produced in years with good weather conditions can be used as marker rings
How can you determine the age of a tree?
start with living trees, then correlating the rings with dead trees, fossilised timber or wood artefacts
- a particularly wide ring = year of favourable growth, would then be used to find the same ring and then compare on a trunk used in an ancient structure
what are limitations with dendrochronology?
particular conditions necessary do not occur often, timber rarely preserved for more than a few thousand years
what is dendrochronology?
a method of determining the age of wood by counting the annual growth rings in the timber
- also called tree-ring dating
why do absolute dating methods all have limitations?
because they rely upon the occurrence of a particular set of circumstances before they can be used
what is relative dating?
determine whether one sample is older or younger than another
- it is not possible to determine the actual age of a fossil or artefact using this technique, but useful in enabling a sequence of events to be established
what is stratigraphy the study of?
the study of rock layers (strata)
what is the principle of superposition?
- assumes that in layers of sedimentary rock the layers at the top are younger than those beneath them
any fossil found in the top layer will be younger than material found lower down
what are limitations to stratigraphy?
-distortion of the Earths crust occurs and rock layers may be turned upside down, possible for fossils or artefacts to be buried by animals or by early humans some time after the deposition of sediment (specimen may be younger than layers above it
how is stratigraphy used for the correlation of rock strata?
- involves matching layers of rock from different areas
- examining rock itself and studying fossils it contains, comparing index fossils and rock qualities to determine the correlation between different regions of rock
What are index fossils?
widely distributed, present on Earth for a defined and limited period of time –> makes relative dating of strata more precise, used to compare strata from different localities
what are fossilised pollen grains?
- can often be useful as index fossils
- enables a botanist to construct a picture of the type and amount of vegetation existing at the time a deposit was laid down
- gives an image of the climatic conditions existing at the time –> used to then confirm or refute dates at by other methods
what is fluorine dating?
-another relative dating technique, based on the fact that when left in soil, fluoride ions (present in water) will replace ions in the bone
how does age affect the amount of fluorine present in a fossil?
the older the fossil, the more fluorine it contains –> allows relative ages to be established
What are limitations to fluorine dating?
- concentration of fluoride in ground water varies from time/location
what is the geographical time scale measured in?
eras–>period–>epochs
what four conditions need to be present for a fossil to be formed?
- a quick burial
- the presence of hard body parts
- an absence of decay organisms
- a long period of stability - the organism needs to be left undisturbed
