variation in populations

* means that you don't need to know it.

species

a group of similar organisms that can interbreed in nature and produce vigorous, fertile offspring

→ means that their offspring will survive to reproductive age and then produce offspring of their own that can also reproduce

subspecies

different races of the same species, who do not interbreed directly, but gene flow still exists

e.g. tigers: bengal, siberian, simatran

they can technically interbreed but they don’t really because their geographic location is different

extinction

the permanent loss of a species

no evidence or sightings for at least 50 years

if referring to small group, say extinction of population

population

a group of organisms of the same species living in a defined geographic region at the same time

e.g. wombats: population of northern hairy-nosed wombat

gene pool

the genetic makeup of a population; includes the sum of all the alleles for different genes present in a population

→ basically all of the alleles that are present for the different genes within that population makes up their gene pool

What is an allele?

a different variation of a gene. genes code for proteins, so we have somewhat different proteins produced in different individuals

gene flow

the movement of genes and alleles between populations.

gene flow increases the genetic diversity within a population

why is variation important?

important for a population to survive any sudden change in their environment

*variation occurs when members of a population display different phenotypes (traits)

e.g. *physiological, structural or behavioural traits.

sources of variation

• reproduction → passing alleles to offspring

• gene mutation/mutation in alleles

• environment causes phenotypic variation (e.g. tanning)

2. How can you measure genetic diversity?

by examining the gene pool of a population and calculating the allele frequency

What does it mean if a population has a wide range of alleles?

they are genetically diverse

For Hardy Weinberg what does P and q mean?

P - dominant allele

Q - recessive allele

genetic drift

the random changes in allele frequency due to chance events

What kind of population does genetic drift have a more pronounced effect in?

more pronounced effect in small populations, and this can result in the loss or fixation of an allele

• this results in reduced genetic diversity in small populations.

in this pic, blue is fixed and red is lost ☹

types of genetic drift/allele frequencies changing in a population

founder effect, bottleneck effect

the founder effect

occurs when a few individuals migrate to create a new population in a different geographic location that is not representative of the original population

allele combinations are different from original population AKA the individuals are genetically different to the og population, resulting in a different gene pool → *they will be very different genetically

since there are only a few founding individuals, there will be very low levels of genetic variation

*it’s basically the result of inbreeding?😟

the bottleneck effect

the severe reduction of individuals in a population generally due to a catastrophic event such as disease, bushfire, or human impact

population will increase in numbers over time, but genetic variation stays low as the gene pool only comes from surviving individuals

→ *inbreeding again 🤕

3. Fossil record

fossils appear in an order of ‘fossil succession’ from single cellular organisms to structurally complex multicellular organisms

several mass extinctions have occurred throughout Earth’s history

What opportunities do mass extinctions provide?

mass extinctions provide opportunities for other species to thrive and diversify

fossil

the remains of an organism or direct evidence of its presence on Earth

Is the fossil record complete, and why?

it is incomplete because:

• most organisms do not get fossilised due to the conditions required to do so

• or the fossils are too old so the DNA is degraded and scientists are unable to identify the organisms and where it fits in the fossil record

Where are most fossils found?

in sedimentary rock

How are fossils mostly formed?

through the process of mineralization, where

• hard body parts are replaced by hard minerals as the surrounding sediments turn into rock

Why do we not find fossils in igneous (volcanic) rock?

it’s probably too hot so they js die

conditions for fossilisation (RUD)

fossilisation is very rare, but when it does happen:

Rapid burial - covered in sediment; usually underwater. it gently overlays body

Organisms lies Undisturbed - no predators, no earthquakes, etc. do not want disturbance

Decomposition is prevented - bones/hard parts. Low O2, low temp, low moisture, to prevent bacterial decomposition

types of fossils

body, trace, index, transitional

body fossils

fossils of the actual organism

e.g. bones, teeth and claws

soft tissues such as skin, muscles, and organs are very rarely fossilised

trace fossils

not the actual organism. e.g. burrow, footprint, faeces

index fossils

a fossil that:

• had a wide geographic distribution

• existed for a relatively brief period of time

fossils that are found in the same rock layer can be estimated to be the same age.→ form of relative dating

transitional fossils

intermediate forms of organisms that provide an evolutionary link between species.

dating techniques

relative dating, absolute (radiometric) dating

relative dating

• the age of the rock is determined by comparing it to another rock

• stratigraphy/stratification:

  • the study of the sequence of rock layers (strata) in any one area

  • layers deposit over time

  • older layers are lower

uses index fossils → fossils in the same layer estimated about same age

⭐️ a fossil’s relative age is provided!

absolute (radiometric) dating

• provides a numerical (absolute) age for a fossil

• based on radioactive isotopes and their half-lives

• half life - the time taken for half of the parent isotope to decay into its daughter isotope

describe the difference between relative and absolute dating

relative:

• uses the Earth’s layers to determine whether one fossil is older than another based on the position in the rock layers. (older fossils lie deeper than younger fossils)

absolute:

• uses the decay of certain elements to calculate the actual age of a fossil. (half life = time taken for half of a sample of atoms to decay.

carbon dating

dating organic fossils that contain carbon. they must be less than 50,000 years old, otherwise radioactive isotope cannot be isolated.
it is easy to extract carbon from mummified carcass

4. selection of phenotypes

why are some individuals more likely to survive

some individuals are more likely to survive change in their envronment due to a particular phenotype

How does variation exist in the population?

through mutations that may have created new alleles or by different allele combinations in sexual reproduction.

Recall the process of Natural selection, what variation means for individuals in a species, and what the result of this is

variation exists in individuals within a species that may lead to an advantage if a change in the environment occurs

a selection pressure present in the environment acts on that variation

→ this means some individuals in the population have a survival and reproduction advantage

individuals that survive pass on the allele to the next generation through reproduction, resulting in more individuals with the trait.

→ this results in increased allele frequencies for the trait in the population

it acts on certain individuals in a population, not the whole population

selective breeding

a human (usually a farmer) selects the trait that is desired based on phenotype

• selects two organisms that display the trait, and breeds them → to increase the chance of offspring having these traits

• observes the offspring, and then selects the offspring with the best version of the desired trait. Breeds the offspring

completes the process many times until the trait is observed in all offspring

selection pressures *

• predators

• availability to resources (water, shelter, mating habitat)

• food sources

• disease/pathogenic spread

• environmental phenomena (natural disasters)

• weather conditions/changes (e.g. floods, storms, etc)

• abiotic conditions (e.g. temp, CO2 concentrations)

half life

the time taken for half of the parent isotope to decay into its daughter isotope

half life of carbon?

approx. 5730

speciation

process by which new species are formed

what is allopatric speciation?

speciation due to geographic separation

Steps for allopatric speciation

1. There is variation and gene flow in a population living in a specific geographic area

2. A geographic barrier separates the population (e.g. a river *or mountain range forms), and gene flow stops

3. Different selection pressures on either side of barrier. Different phenotypes are selected for on either side

4. Over time, many different mutations occur in the different populations, and they accumulate resulting in phenotypic differences

5. The two population become so different that they become reproductively isolated. If the two populations were brough back together, they could not interbreed. A new species has formed

Galapagos Finches

acestral finch arrived from mainland South America and increased in population. Some of them flew to other islands with different selection pressures like food source.

Over time, the beak shapes changed and the finches became so different on each island that they became different species

Sympatric speciation

speciation due to reproductive separation

Steps of sympatric speciation

1. There is variation and gene flow in a population living in a specific geographic area

2. A reproductive barrier prevents some members of the population from reproducing, such as mating at different times of the year

3. Over time, many different mutations occur in the different populations, and they accumulate resulting in phenotypic differences

4. The two populations become so different that they become reproductively isolated. Although the populations live in the same niche, they cannot interbreed. A new species has formed!

Howea palms- Lorde Howe Island

example of sympatric speciation, when two species from a single ancestor form in the absense of a geographical barrier.

the two species diverged after they began flowering at different times of year, as a result of soil preferences

selection pressure

a factor in an organism’s enironment that will result in the death or inability to reproduce for unsuited individuals

What genetic evidence could show that two populations are different species?

Scientists could compare:

• DNA sequences

• mitochondrial DNA or

• conduct comparative genomics.

Significant genetic differences indicate long-term reproductive isolation, supporting that the populations are separate species.

structural morphology

the study of the size, shape and structures of plants, animals, and microbes, as well as the interactions between their parts

this helps us determine whether there is a common ancestor or not

THIS IS HOMOLOGOUS, AND ANALOGOUS

Homologous structures

• have the same structure but may have a different function

• evidence of different selection pressures

• evidence of a common ancestor (divergent evolution)

*example: pentadactyl structure: people’s arms, bats wings

Analogous structure

• a different structure but the same function

• due to similar selection pressures

• no common ancestor

example: flippers/fish tails. they look different but they all need to swim

Vestigial structures

a feature that a species inherited from an ancestor but that is now less elaborate and functional than in the common ancestor.

*→ the selection pressure for that feature to be maintained is no longer there

example: whales still have a pelvic bone but it’s very small due to lack of selection pressure (e.g. live in water vs on land)

Molecular homology

the study of the similarity or difference of molecular information, using nucleic acid or amino acid sequence

Advantages of using nuclear DNA

• large number of genes to compare because there are more nucelotides vs amino acids, and therefore greater comparison

• higher variability than amino acids as genes will contain introns and exons

  • more variablity in introns compared to exons, as they don’t code for the protein, as it will not affect function

• changes in nucleotides don’t always mean a change in amindo acid: redundancy/silent mutations

• recombination occurs: *can account for variability within a species

  *higher chance of degrading

advantages of using mitochondrial DNA

• maternal inheritance; no complication of recombination compared to nuclear

• smaller number of genes

• a positive: there is large number of copies per cell compared to nuclear

→ *less likely to degrade

Amino acids

• changes in amino acids may indicate a function change in the protein

• sequences are smaller: 1 amino acid for 3 nucleotides,

• may increase sensitivity of analysis as there are 20 amino acids compared to 4 nucleotides

• more conserved than DNA due to amino acids making up the protein and it is important to maintain specific shapes for function

what do you do in sequence alignment

compare the sequences and identify differences and similarities

Molecular clock theory

• the greater difference in the nucelotide/aminoacid sequence indicates

• there has been more time for mutations to occur and accumulate and more time since divergence from a recent common ancestor

Phylogenetic trees

• a diagram showing evolutionary relationships; can be for a single gene or genome

• usually created with molecular evidence; nucleic acid or amino sequences, but can be created based on structural evidence as well

8. mammals

a class of animals with vertebrae

shared features of mammals

• mammary glands to feed young milk

• have hair/fur on surface

• three middle ear bones

• sweat gladnds

• all give birth to live young (except monotremes)

• neocortex region in the brain (sensory perception, cognition, spatial reasoning)

Primates

evolved from ancestors that lived in trees

Primate characteristics

• prehensile hands and feet with fingertip pads that are sensitive

• opposable thumbs (allows power grip and precision grip)

• fingernails instead of claws

• well developed collar bone and rotating shoulder joint

• large forward facing eyes protected by bony eye socket

• separated big toes that face forwards

• large brain volume compared to body size

• penis and testes that permanently hang down from the body

Hominoids - “Apes”

gibbons, orang-utans, chimps, gorillas, and humans

• excludes monkeys

Features of hominoids

• no tail (monkeys have a tail)

• long arms

• full rotation of shoulder joint

• broad pelvis

• upright (or semi-upright)

• wide shallow chest cavity

• larger brain relative to body size compared to other primates

  • increased complexity of cerebrum

  • increased intelligence (problem solving etc)

Hominids - Great Apes

orang-utans, gorillas, chimpanzees and humans

Hominini

taxomic tribe

• homo sapiens and extinct hominins

• chimpanzees

Hominins

all human species and their bipedal ancestors

Features of hominins

• bipedal; walk upright

• arms shorter than legs

• not much hair

• more sweat glands

• wrists and hands can rotate and manipulate objects

• have relatively large brains to body size

• cultural evolution

• arched foot

• smaller canine teeth

• no tail

• big toe more in alignment with other toes

• opposable thumbs but not toes

9. evidence for hominin evolution

skull changes, brain volume, cerebral cortex, cultural evolution

major trends in structural evolution of the skull in hominins

• reduced brow ridge

• loss of the large bony crest on top of skull

• flatter, smaller faces

• reduced zygomatic arches and sagittal crest

• reduced jaw bones

• reduced jaw muscles

Hominin features other than skull and cognitive that show evolution

• development of larynx and associated muscles

  • speech

• hair reduction due to less parasite infestation, thermoregulation

• more sweat glands; greater endurance

Major changes in evolution of the brain in hominins

• larger brain cavity size relative to body size and therefore an inferred larger brain size

• increased cerebral cortex so and complex thought

delete

increased cerebral cortex and complex thought

Cultural evolution

• the passing on of information; teaching

• due to changes in biological evolution; brain capacity and pharynx/larynx

includes:

• travel

• language and communication

• passing on of knowledge

• food, art, music, etc

• traditions, beliefs, religion

10. Types of evolution

• biological evolution

• cultural evolution

• functional changes

• structural evolution

• cognitive changes

Biological evolution

changes in the DNA that results in changes to morphology and structure

Structural evolution

changes in anatomy especially bones e.g. changes in foot, spine, and skull structure

Functional changes

changes in the way the organism operates e.g. changes in biological systems

Cognitive changes

changes in brain size and complexity and consequently thinking processes

cultural evolution

the passing on of information (teaching) between generations

Evidence for bipedalism - head/skull

• foramen magnum has become centralised

• allowing attachment of spine and spinal cord directly under the skull

Evidence for bipedalism - spine

• change in vertebra and spinal column

• S shaped spine in homo sapiens, allows to stand fully upright and bring spine under the centre of skull. it helps for weight to be distributed evenly

Evidence for bipedalism - pelvis

pelvis has become broader and more compact; bowl shaped

• better weight bearing capacity

• allows an upright stance

• more support and space for organs

• wider attachment of femurs (thigh bone)

Evidence for bipedalism - femur

femur is more angled towards the knee, this allows for a smooth bipedal motion

Evidence for bipedalism - foot

• big toe aligned to the other toes, which allows for better heel strike when bipedal; more efficient gait

• big toe helps push off the ground

• arched foot helps with a more efficent stride/gait

Hominin arms

• structure of collar bone, shoulder blade, and arm

• shoulder joint point sideways, but in older hominins more upwards

Evolution of the hominin hand

• change in hand proportions - larger thumb more closely aligned to finger lengths

• thumb musculature increased; greater load

• wrist mobility has increased

• finger bones have decreased curvature

• sensitiveity of fingertips

There is often disagreement about new fossils and where they belong in human evolution. Why?

• the fossil record is incomplete (and there is a lack of viable DNA evidence) which results in different interpretation of evolutionary links

• as more evidence (fossil and DNA) is discovered, our understanding of human evolution is altered

How do we know about our history of interbreeding

analysis of mtDNA and nuclear DNA has indicated genetic relationships between Homo neaderthalnsis and early modern humans (Homo sapiens)

How much Homo neanderthalensis DNA in our populations?

Genomes of European populations and Asian populations contain approximately 1-3% Homo neanderthalensis DNA

What populations share DNA with Denisovan

papuans, some Polynesians and Indigenous Australians share DNA with Denisovan

What two species also interbred

Denisovan and H. Neanderthals

Human migration - where did it start and what occurred during this time

• Early hominins evolved in Africa, and began migrating out of Africa as early as 2 million years ago. Homo Sapiens started migrating out of Africa around 150,000 years ago into Europe and Asia first

• gene flow occurred during this time, and DNA evidence shows interbreeding between homo sapiens and homo neanderthalensis

Human migration - when and how did they arrive to Australia + evidence BITCHHH

• modern hominins arrived in Australia approximately 65,000 years ago through South East Asia - via existing land bridges

• groups migrated down the east and west coasts of Australia rapidly after arrival

• Australian megafauna e.g. Diprotodon - a large womabat shaped animal, became extinct around 42,000 years ago, giving evidence for rapid migration of humans around Australia

Where and how did Aboriginal and Torress Strait Islander peoples migrate to the Australian continent?

migration for these travellers was a difficult task

aboriginal and Torres Strait Islander people arrived from Sunda which was separated from Sahul and Australia by a great expanse of water

Sahul and Australia were connected by a land bridge at the time; this is now under water ☹

What evidence supports the prolonged connection of Aboriginal and Torres Strait Islander Peoples with the Australian continent?

evidence including cultural artefacts, demonstrate a prolonged connection with specific populations in Australia, in agreement with Aboriginal and torres Strait Islander People’s cultural beliefs, and connection with Country and Place