evolution

alleles-

· Heritable characteristics are encoded for by genes and may be transferred between generations as alleles

Evolution

· change in the allele frequency of a population's gene pool over successive generations

gene pool

· all the genes and their different alleles, present in an interbreeding population.

allel freq in large vs small populations

· Large populations- high amounts of genetic diversity, increasing the chances of biological fitness and survival
· small gene pool- low genetic diversity, reducing biological fitness and increasing chances of extinction

how does evolution occur

· Mutations\=new alleles
· Selection pressures favour some traits
· Barriers to gene flow emerging between different populations

mutation

· Define - change in the nucleotide sequence of a section of DNA encoding for a specific trait

what do they do

· give rise to new versions of a gene (called alleles), change organism
· Increase genetic diversity

can they be passed down?

· Mutations in body cells- cannot be passed down ·  Mutations in gametes/germ line cells- can be passed down

Types of mutations -point

mutation alters adds or removes nucleotide

point mutation- silent mutation

substitution results in new codon, still code for same amino acid

point mutation- Missense mutations

· substitution results in new amino acid (may or may not affect protein function)

point mutation- Nonsense mutations

substitution results in stop codon

point mutation- Frameshift mutation

· Nucleotide added or removed, shift all nucleotides forwards

what do they do

· cause the formation of new codon arrangements (different amino acids created, loss of protein funtion

block mutations-

· mutation effects large segment of chromosome, multiple genes

block mutations- deletion

Sections of a chromosome are removed. Hence, missing genes and serious effect on growth

block mutations-duplication

· Replication of a section of a chromosome. Hence, multiple copies of genes in expression.

block mutations-inversion

Section of the sequence breaks off, rotates 180 degrees and reattaches.

block mutations-translocation

· Usually segments of a chromosome are exchanged with segments of another, i.e. swapping of genetic material.

Gene flow

· Gene flow- movement of alleles between interbreeding populations
· Gene pools can change when new individuals join or leave a population due to migration

Genetic drift

change in allele frequencies in a population due to chance events

selection pressure

- external factors that affect ability for organism to survive and reproduce, reduce variation in gene pool

Bottleneck effect- genetic drift

· Define- random event such as a natural disaster can quickly and drastically reduce the number of individuals in a population, survival of individuals is likely due to chance.
· surviving population has less genetic variability than before and will be subject to a higher level of genetic drift

Founder effect

· Define- small group move to a new location, allele frequency of the new population different to the original population.
· new location \= different selection pressures, further differences in allele frequencies between the populations.

natural selection quick sumary (not on study design)

variation- slight variation within population
selection pressure- kills out some of pop
advantage- those with a small variation that are more liley to survive to selection pressure and pass to offspring, therefor increase in frequency

Selective breeding (artificial selection)

change in gene pool due to human intervention

what happens

· what happens -humans decide which traits are desired, breed these individuals to pass traits on and develop into better strains. Continue until population reliably reproduces the desired trait

why selective breeding in plants

· produce higher-quality food.
· Desired characteristics - large size, higher numbers, better taste and appearance, faster growth, and greater resistance to disease.

why selective breeding in animals

increased size, yiled of meat, resistance to diseases.

Domestication

· selecting for tameness and affectionate behaviours

Hybrid Vigor

cross between two genetically distinct individuals. (eg donkey and horse)
cant interbreed to produce viable offspring

negative impacts of seleticve breeding -Reduced resistance to environmental change-

· Gene pools have low genetic diversity, favourable allels dont pose survival advantage in a changing environment.

Reduced biodiversity

Selective species replacing 'wild' varieties, reducing the number and variability of species used in agriculture. reduces the biodiversity, increasing impact of changeing selection pressures

Increased chance of genetic abnormalities

· Interbreeding between related individuals increases the risk of genetic abnormalities.

Low gen diversity

· Selective breeding increases allele frequency for desired trait, also decreases the frequency for other alleles. This reduces the genetic diversity in a gene pool.

Inbreeding depression

· Inbreeding increases the likelihood of homozygous recessive conditions, many of which are detrimental

this contributes to inbreeding depression.
· Health and life span affected.

Speciation

formation of a new species from a pre-existing species

when does it occur

reproductive barrier between 2 populations, no gene flow

what happens

populations evolve separately as a result of cumulative mutation, genetic drift and natural selection, Eventually populations reach genetic divergence whereby they can no longer interbreed (speciation)

what is a species

· population whose members have the potential to interbreed to produce fertile, viable offspring

Allopatric Speciation

· define- geographical barrier physically isolates the populations of a species

Galapagos finches - case study (study design)

1. finches have specialised beak shapes depending on their primary source of nutrition (e.g. seeds, insects, nuts, nectar)
2. They occupied different islands with no gene flow between populations
3. Over time, this leads to the rapid evolutionary diversification of a single ancestral line (adaptive radiation)

Adaptive radiation

rapid evolution of many related species from a recent common ancestor.

Two factors influenced adaptive radiation (finches)

· Significant environmental selection pressure: different food resources
· Genetic control of beak size and shape: mutations in one regulatory gene had significant consequences for expression of a group of genes involved in beak formation

Sympatric Speciation

· population becomes reproductively isolated without being physically separated

2 types of isolation

· behavioural isolation - closely-related individuals may differ in their courtship behaviour, they only attract members of their own population.
· temporal isolation- populations may mate or flower at different seasons or different times of day.

Case study - howea palms

1. Howea palms are endemic to Lord Howe island but may be exposed to different soil conditions (volcanic vs calcareous)
2. Palms growing in nutrient-rich volcanic soil tend to flower earlier than palms growing in calcareous soil (more basic)
3. palms were flowering at different times, reproduction ceased to be random
4. This temporal isolation between the two populations of palms caused them to evolve along different pathways (i.e. disruptive selection)
5. Over time, the gradual accumulation of genetic differences caused the populations of Howea palms to form separate species

fossil

preserved remains of any organism from the remote past

Types of fossil

· physical - represent actual remnants of life and include body fossils (preserved remains) or petrified fossils (mineralised hard parts)
· biosignatures - represent the chemical evidence of past life and include the products of cell biosynthesis
· Trace fossils- Preserved evidence of an animal's activity or behaviour that do not contain parts of the organism.

Fossilisation

preservation of hardened remains or traces of organisms in rocks.

Process of fossilisation

· Death and decay
· Burial- quickly buried, reducing decay and destruction by scavengers.
· Sediment - sediment solidifies to rock.
· Permineralization -minerals in rock seep into hard remains, and crystallise, making mineral structure in shape of body.
· Discovery- movement of rocks and erosion expose fossil.

fossil record

totality of fossils, both discovered and undiscovered

Law of fossil succession

newer species likely evolved as a result of changes to ancestral species

order of fossil record

· Prokaryotes before eukaryotes · Ferns before flowering plants · Invertebrates before vertebrates

index fossil

· fossil of a known age found in rock layer, allowing for chronological comparisons between different fossils

what do they do

synchronise the age of rock layers between two different regions

to be an index fossil

wide geographical area
relatively short lived

transitional fossils

remains that shows traits common to both an ancestral group and its descendants

they determine links between species through common traits to ancestor and predicted descendants

relative dating

inexact measurement, uses rock layers to assign ages to fossils for comparison

how does it work

Fossils identified as older or younger depending on strata they are in

occasionally, strata for time period is missing due to environmental conditions

index fossils can be used to synchronise the age of rock layers between two different regions

fanual succession

fossils in strata succeed one another in a predictable order, even if they are found in different places.
·age of rock strata can be estimated via comparison of fossils contained in layers.
· Index fossils with a known time range of existence can also be used to estimate the age of the rock layer.

absolute dating

uses the rate of radioisotope decay to determine the exact age of a fossil sample or rock strata

radiometric isotopes

·· decay at constant rate, time taken for half the original radioisotope to decay is known as the half life
· comparing ratio of radioisotopes in the fossils to that found in the atmosphere\= determine life of fossil
· Different radioisotopes have different half lives and are thus useful for dating different types of fossilised remains.

short range dating

· All living things contain carbon
· carbon is a mix of two isotopes - 12C (stable) and 14C (radioactive)
· proportion of 12C (stable) and 14C (radioactive) mirrors environmental levels
· When an organism dies\= ratio changes as 14C breaks down into 14N (beta decay)
· Scientists can measure the amount of 14C remaining in a sample to determine how long ago it died

long range dating

· Define - use of radioisotopes that are not present in fossils or rock strata
· only done on igneous rock around fossil, used to determine age range of a rock strata
· age of fossil then approximated according to the strata in which it is located

comparitive anatomy

· compare structures of two species to understand changes undergone through evolution from common ancestors.

Homologous structures

· Define - features similar in basic structure despite being used in different ways

pentadactyl (5 digit) limb-

· found in most vertebrates, same general bone structure, inherited from a common ancestor, highly modified to serve specialized functions. Eg legs and fins

what do homologous structures indicate

· indicate divergent evolution, as the basic limb plan has been adapted to meet different needs.
· more similar\= more closely related

Divergent evolution

· evolution of two (or more) different species from a common ancestral species.

how

· Populations separate and gene flow cant occur, genetic differences lead homologous features to gradually become different and different functions

Analogous structures

· not all similarities between species are inherited from a common ancestor, they can come from different origins.

what do Analogous structures indicate

Analogous structures indicate convergence evolution
eg bird and butterfly wings

Convergent evolution

· Define- evolution of similar features in unrelated groups of organisms.
· different species are exposed to same selection pressures so that Similar adaptations are favoured during natural selection.
· Eg dolphins and sharks

Vestigial organs and why do they occur

• -no longer perform a function, must have been important at some poin in some ancestral form, but become useless in later species
• how- selection pressure for complete loss is weak, the structures remain in a reduced form.

Molecular homology

· study of the similarity of patterns in the nucleotide sequences of DNA or amino acid sequences of polypeptides as evidence for a common evolutionary origin.

how

differences between comparable base sequences demonstrates the degree of evolutionary divergence, more differences between base sequences\= more time past since two species diverged, more similar base sequences of two species, more closely related they are

Scientists use non coding DNA

· Why- more mutations, these Gene sequences mutate slower, as changes to base sequence affect protein structure and function, used more more closely related organisms

They also use amino acid sequences

· Use them less- have the slowest rate of change due to codon degeneracy
· They are used to compare distant organisms

Mitochondrial DNA- what and why

· What is it- double stranded circular dna, does not undergo crossing over, high mutation rate and can be used as a molecular clock to compare closely related species
· What's it used for- tracing evolutionary relationships within a species, more mutations \= more distantly related

Benefits over DNA

· Maternal inheritance - inherited from mother only, more direct genetic lineage
· No recombination - no recombination occurs, maintaining sequence fidelity
· Stable mutation rate - sequences mutate at a higher rate
· High copy number - every cell has mitochondria, large amounts of mtDNA gathered

Amino acid comparison

· closely related species have proteins with more similar amino acid sequences.
· Amino acid sequences made by genes and mutations.
· Degree of protein similarity is determined by mutations
· More time \= more time for mutations to occur, leading to greater differences in amino acid sequence

Phylogenetic trees

branching diagrams that depict the evolutionary relationships between different groups of organisms

Cladogram-

· evolutionary branches to show how each species is formed

clade

ancestral organism and all evolutionary descendants, they possess common characteristics

nodes

· branches that represent speciation event which species are formed (divergent)
· Less nodes\= more closely related

Phylogram

· - branch lengths may differ according to the length of time since speciation, comparison of sequences that have constant rate of mutation
· Compared to clado- they do infer time, clado don't

defining humans

- bipedal hominoids that belong to the class Mammalia and the Order Primates

mammals

group of vertebrate animals that have hair and produce milk to feed young

trends in human evolution

· Increasing brain size (brain case volume)
· Shorter arms, longer legs re. body size
· Smaller teeth, reduced jaw muscles
· Less migration, more communal living

2 main changes

· Bipedalism-suited to travelling long distances in open areas
· larger brains- increase problem-solving and communication

main changing enviromental pressures

· Changes to the climate in East Africa \= decline of food-rich jungle habitats, and the spread of open wooded grasslands.

change to skull

· Larger brain case- due to increasing brain size, not s specific survival advanateg
· Smaller jaw- changes to diet, allow expansion of brain case of skull

Human natural selection

· Variation-in brain

Other skeletal changes

· SPINAL CORD-S- curved spine for better weight distribution over pelvis
· PELVIS- Narrower and deeper, to change the angle of the femur at the knee
· RELATIVE LENGTH OF LIMBS- Arm bones shorter, Leg bones longer increase in height
· FINGERS- Short straight finger bones, increased grip and better manipulation of tools
· TOES- Shorter toes, big toe fully aligned with other toes for stability

Genus Australopithecus

· 2-4.2 mil years
· East and south Africa
· Small brain, long arms

Genus Paranthropus

Homo habilis

· 1.4 - 2.4 mil
· Eastern and southern Africa
· Key characteristics:
· larger brain case than earlier species
· Early tool use
· ape-like features (long arms, forward-projecting jaw)

Homo erectus

· 143 000 thou - 1.89 mil years
· North, eastern and southern Africa, west and east Asia
· Larger braincase than predecessors
· Similar body proportions to modern humans
· First Homo species to migrate out of Africa
· Social behaviours, caregiving
· Constructed stone tools, shared expertise
· Evidence of cooking food