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135 Cards in this Set

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A particular characteristic that a gene codes for.

-is inherited


A different form of the same gene.

Two alleles for the same gene would differ slightly in their nucleotide sequence.


The combination of alleles that make up an individual


The observable traits of an individual.

Usually caused by a combination of genotype and environment.

Gene pool

All the alleles within a population.


Apermanent change in a genetic sequence, including changes to the nucleotidesequence or chromosomal arrangement.

How do mutations occur?

They can occur spontaneously, or they are induced by a mutagen/environmental factor. They can also accidentally occur during DNA replication.

Germline mutations

Occur in gamete cells and hence can be passed on to the next generation.

Somatic mutations

Occur in body cells and cannot be passed on to the next generation.

Point mutations

Mutations in a gene involving the alteration/adding/removing of a single base in the DNA sequence.

Can be substitution or frameshift mutations.


-Replacement of one nucleotide for another.

-Can be missense, silent or non-sense mutations.

Missense mutation

Causes the codon to read for a different amino acid. These mutations still produce a protein.

Silent mutation

Occurs when a substitution results in a new codon that still codes for the same amino acid.

Non-sense mutation

Whena substitution mutation results in the creation of a stop codon, it isclassified as a nonsense mutation, because no other amino acids will be addedafter this point.

These can have severe effects, especially if the stop codonis implanted early on, as they may not be able to fold correctly.

Frameshift mutations

Involve one or two nucleotides being either added (nucleotide insertion) or removed (nucleotide deletion) from a nucleotide sequence, altering every codon in that sequence from that point onwards.

Block/chromosomal mutations

Mutations that affect large sections of a chromosome, typically multiple genes. Can occur during meiosis or by mutagens.

There are five main types: duplication, deletion, inversion, insertion and translocation.


involve the replication of a section of achromosome that results in multiple copies of the same genes on that chromosome


removesections of a chromosome


a section of the sequence breaks off the chromosome, rotates 180 degrees and reattaches to the same chromosome


occurswhen a section of one chromosome breaks off and attaches to a differentchromosome.


awhole chromosome or a segment of a chromosome becomes attached to or exchangedwith another chromosome.

Chromosomal abnormalities

-Involves a whole chromosome or part of a chromosome

-Can be detected by a karyotype

-Includes aneuploidy and polyploidy


The presence of an abnormal number of a particular chromosome

Can be either an extra chromosome (called a trisomy when there are three copies of one chromosome) or a missing chromosome.

Caused by non-disjunction during meiosis.


-Where there are additional sets of chromosomes (more than two).

-Instead of diploid, it could be triploid or tetraploid etc.

-Can be caused by hybridization or diploid/haploid gametes (triploid) or diploid/diploid gametes (tetraploid) fusing.

Polyploidy: if the number of sets of chromosomes is....

-even, the organism is fertile

-odd, the organism is infertile

Natural Selection

-is the influence of environmental pressures on allele frequencies.

-these pressures (selective pressures) mean that some individuals are better at surviving and reproducing and hence are more able to pass their genetics on to the next generation.

Types of environmental pressures

Temperature change

Mate availability

Predator abundance

Gene flow

Gene pools canchange when new individuals join the population from a different gene pool orwhen some individuals leave a population (immigration and emigration).

This migration of individuals canresult in gene flow.W

hen gene flowexists between two different populations, the gene pool may remain fairlysimilar. When gene flow is not possible between populations, the gene pools aresaid to be isolated.

Genetic drift

Allele frequenciesin a gene pool may also change randomly over time as a result of chance events,this is known as genetic drift.

Genetic drift is more clearly seen in smallpopulations, with little to no gene flow, as the random death of one individualcan significantly alter allele frequencies.

Genetic drift canoccur when populations decrease for a period of time (bottleneck effect) or insmall founding populations (founder effect)

Bottleneck effect

The number ofindividuals in a population can be drastically and quickly reduced as a resultof a random event, such as a natural disaster.

The bottleneckeffect describes the impact on the remaining population.

Because of the reducedpopulation size, the possible reproductive pairings are limited, which leads tohigh levels of inbreeding.

Inbreeding resultsin reduced variation in the population and an increase in the number ofhomozygous individuals. This lack of variation makes the population morevulnerable to environmental change.

Founder effect

The founder effectoccurs when a small group of individuals from a larger population move to a newlocation and establish a new population.

If a small portion of a populationbecomes seperated from the original population, their smaller gene pool is unlikelyto reflect the allele frequency of the original population.

There is anincreased risk of inbreeding and less variation.

In the newenvironment, the environmental pressures on the founder population are likelyto be different from those experienced by the original population.

Thesedifferences in environmental pressures drive further changes in allelefrequencies and, ultimately, evolution.


The change in allelic frequencies over time.


A group of individuals that are genetically similar enough that they can produce viable offspring when interbreeding.

Factors causing genetic variation

-Mutation (change in DNA)

-Gene flow (exchange of genes between populations)

Factors causing selection of certain alleles

-Natural selection

-Genetic drift

Selective breeding

Where humans decide what individuals will breed and leave viable offspring. This is usually used to increase desirable traits in a population.

Basic steps of selective breeding

1. Determine the desired trait

2. Interbreed parents who show the desired trait

3. Select and interbreed offspring with the best form of the trait.

4. Continue the process until the population reliably reproduces the desired trait.

Selective breeding causes reduced resistance to environmental change

A population with low genetic variation is one in which all the individuals are very similar.

As long as the alleles in the gene pool have a high adaptive value for the environmental conditions, the species will persist.

However, should the environmental conditions change, it is unlikely that the same alleles will still have the same adaptive value.

A single disease could potentially wipe out entire populations if none of the individuals are resistant.

Selective breeding reduces biodiversity

Selectively bred species are also replacing wild varieties, reducing biodiversity.

This, combined with low genetic variations within the selectively bred populations, puts global food security at great risk.

Selective breeding increases genetic abnormalities

Selective breeding can increase genetic abnormalities.

Many of these abnormalities are recessive conditions, meaning that an individual must have two copies of the same allele.

Inbreeding and small gene pools greatly increase the frequency of particular alleles, increasing the likelihood of homozygous recessive conditions.

Prezygotic isolating mechanisms

Thosethat typically prevent individuals from different populations frominterbreeding; in other words, they prevent fertilisation from occurring in thefirst place.

Types of prezygotic isolating mechanisms

Geographical isolation: populations are separated by physical and geographical barriers, such as oceans.

Ecological isolation: populations occupy different niches within the same ecosystem.

Temporal isolation: the breeding cycles or active times of populations do not overlap.

Behavioural isolation: this occurs when mating calls and courtship rituals are highly specific.

Structural or morphological isolation: the reproductive organs of different species are physically incompatible and individuals are unable to mate.

Gamete mortality: egg and sperm fail to fuse in fertilisation.

Postzygotic isolating mechanisms

Those that typically prevent a zygote of two different species from developing into a fertile adult.

The offspring resulting from interbreeding between individuals from different species are called hybrids.

Types of postzygotic isolating mechanisms

Hybrid inviability: the mechanism of reproductive isolation in which the sperm from one species does successfully fertilise the egg of another species to form a hybrid zygote, which has unmatched chromosomes.

Sometimes the zygote survives and undergoes cell division but the offspring does not develop fully and will not reach adulthood due to reduced hybrid viability.

Hybrid sterility: the hybrid organism develops but is incapable of reproducing In some situations, the first generation of hybrids are semi-fertile. However, the second generation is generally infertile, known as hybrid breakdown.

Allopatric speciation

variation in a population


population splits


allopatric speciation


causing reproductive isolation and no gene flow


divergent evolution in different environments due to different selection pressures


formation of two different species over many generations


they can no longer interbreed

Geological timescale

-covers from when the earth was first formed through to present day

-constructed in the order of sedimentary rocks laid down over time, in which fossils are found

(shallowest layer = most recent/ deepest layer = oldest)


rock layers

Sedimentary rock

formed by deposition and cementation of minerals

Igneous rocks

formed from molten magma

Geological time scale subdivisions





Precambrian Time

-80% of the geological record

-before complex multicellular organisms

-time before the cambrian

The Precambrian

The period of Earth's formation is referred to as the Precambrian time.

It is divided into three parts: the Hadean, the Archaean, and the Proterozoic eon.

The Palaezoic Era: Cambrian period

Dramatic increase in the number and complexity of life forms in the ocean

Fossils include worms, jellyfish, brachiopods, anthropods.

More diversity in fossils due to the emergence of hard exoskeletons

The Palaezoic Era: Ordovician period

Seas were widespread and rich in algae

Trilobites diversified, as did coral

Provides evidence of the first vertebrates, jawless armoured fish

Ended due to a major ice age

The Palaezoic Era: Silurian period

-earliest evidenceof life on land from terrestrial rocks

-millipedes,centipedes, earliest arachnids appeared

-vascular plantsappeared

The Palaezoic Era: Devonian period

Free-sporing vascular plants began to spread across dry land, formingextensive forests which covered the continents.

By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearingplants appeared.

Various terrestrial arthropods also became well-established.

The Palaezoic Era: Carboniferous period

-emergence of land-based plants and animals resultedin organic matter

-diversification of fish

-jawed fish evolved

The Mesozoic era: Triassic period

-warmer, drierclimate eliminated polar ice caps

-seed plantsfavoured\

-more herbivores

The Mesozoic era: Jurassic period

-dinosaurs thrivedin warm, forested earth

-Pangaea broke upinto two landmasses

The Mesozoic era: Cretacous period

-dinosaur diversityreached peak

-gondwana andlaurasia continued to break up

-small primitivemarsupials were widespread

The Cenozoic era: Palaeogene period

-mammals began totake advantage of niche left by extinction of dinosaurs

-birds becameabundant as new plant life evolved

-continents moved tonew latitudes, affecting ocean currents

The Cenozoic era: Neogene period

-further majorcontinental movement

-modern forms ofmammals, birds and flowering plants evolved

The Cenozoic era: Quaternary period

-drier climate,causing rainforests to shrink

-ice Age extinctionoccurred

-water froze intoice sheets and expose land bridges

Types of evidence for evolution used:



-Structural morphology

-Developmental biology


the study of ancient life represented by fossils

The fossil record refers to the total number of fossils that have been discovered, providing evidence to the evolution of living organisms through geological time

Allows us to know about the kinds of organisms that lived in the past, what they looked like and where and when they lived, allowing us to put a time scale on evolution.


the preserved remains, impressions or traces of organisms found in rocks, amber, coal deposits, ice or soil


the preservation of the hardened remains or traces of organisms in rocks

Process of fertilisation

-has a chance of occurring when an organism is buried by sediments, reducing the chance of decay, due to lack of oxygen for decomposers, and hides the organism from scavengers.

-When sediments accumulate over the organism, the organism is preserved, and as the temperature increases, the soft sediments become solid rocks.

When was the rise of multicellular animals?

The Ediacaran period

When were the first animals on land formed?

Silurian period

When did the first flowering plants develop?

Cretaceous period

When did the first mammals develop?

Cenozoic era, in the Palaeogene period

Likeliness of fossilisation

-small chance

-soft-bodied organisms are unlikely to be preserved, as they decay readily and are more subject to predation

-fossilised parts of plants do not decay readily, as wood/leaves/spores/pollen are resistant to decay

-organisms on land are less likely to be preserved than those in aquatic environment

Impression fossils

Are left when the entire organism decays but the shape or impression of the external or internal surface remains.

If the vacant space of the mould is later filled with foreign material, a 3D sculpture of the organism is formed, known as a cast fossil.

Mineralised fossils

Occur when minerals replace the spaces in structures of organisms such as bones.

Minerals may eventually replace the entire organism, creating a replica of the original fossil, known as mineralisation or petrification.

Mummified organisms

Arethose that have been trapped in a substance under conditions that reduce decayand so are changed little.

Relative dating (using stratigraphy)

-Igneous rocks do not contain fossils, so they are used as a reference point to compare the age of sedimentary rocks that contain fossils

-Theage of a fossil is estimated relative to the known age of the layers of therock above and below the layer that the fossil is found.

-Based on stratigraphy, which is the study of the relative positions of the rock strata, some of which contain fossils.

- The lowest strata is the oldest and the upper strata are progressively lower.

Problems with relative dating

Buckling of the earth


Reburial can cause the geographical sequence to be destroyed

Index Fossils

Afossil of known age found in a particular type of sedimentary rock layer. Itcan be used to indicate the age of the deposit at any single locality in whichit is found.

Can be used in conjunction with stratigraphy to identify particular stratum and hence the age of the fossil.

Absolute dating by radiometric methods

Radiometric methods enable the absolute dating of geological age.

Based on the principle that radioactive elements decay into different elements at rates that are constant for the given element.

Hence, particular radioactive elements/isotopes are used for fossils depending on the time scale involved.

Radioactive isotopes

Decay is constant and independent of the type of rock or environmental conditions they are exposed to.

Absolute dating is based on the half-life of the isotope


the time taken for half the atoms in a sample to decay or have half the radiation

Radiocarbon dating

-used for fossils containing carbon

-involves calculating the amount of decay of the carbon isotope carbon-14

Absolute dating using thermoluminsecence

-can be used to date objects such as pottery, cooking hearths and treated tools up to 500,000 years old.

-it is the emission of light from a mineral when it is heated

-the amount of light is proportional to the amount of radiation an object has absorbed

-the older the object, the more light it emits

-the intensity of the light can be calibrated to determine how much time has passed since the object was heated

-used to date artefacts related to human evolution


-is the study of the distribution of organisms

-distribution patterns give clues to the evolutionary history of organisms and of the Earth itself

-interested in how similar animals are that are found in different parts of the world

Explanation by continental drift

1. geographic split of ancestral species

2. causing isolation of populations on different land masses

3. over time, the species evolved and eventually became seperate species

Comparative morphology

Comparing thestructures found in different organisms

Comparative anatomy: homologous features

-have the same fundamental similarity in structure but different functions

-they are evidence of common ancestry and divergent evolution

Comparative anatomy: analogous features

-have the same function but do not have the same structural similarity

-evidence of convergent (same solution arising in evolution to a particular situation)

eg. wings/eyes

Vestigal structures

-is a reduced structure with no apparent function

-is the evidence of evolutionary relationships

-shows that an organisms has diverged from a common ancestor.

Developmental biology

the field of biology that studies the process of how an organism changes from a zygote to the form of an adult

Comparative embryology

-embryonic development is controlled by a series of master genes that organise the position and rate of cell growth

-organisms that share a common ancestor often have similar master genes, and hence the embryo will pass through similar stages of development

Darwin's Theory of Evolution: Mechanisms behind the theory

-members of a population often vary in their inherited traits

-all species produce more offspring than their environment can support, and most of these offspring fail to survive and reproduce

Darwin's Theory of Evolution: the implications of the above mechanisms

-individuals whose inherited traits give them higher probability of surviving and reproducing in an environment will tend to leave more offspring than others

-this unequal ability of individuals to survive and reproduce will lead to the accumulation of favourable traits in the population over generations

Divergent evolution

Is the evolution ofdifferent species (populations) from a common ancestral species (population)

This is where two populations of a species have become separated through geographical isolation. Time has passed and natural selection as well as genetic drift has led to the two populations become seperate species.

Adaptive radiation

the rapid divergence of evolutionary lineage from a recent common ancestor usually caused by a change in the environment or colonisation of a new environment

Convergent evolution

is the development of similar features separately in unrelated groups of organisms that don't share a recent common ancestor

This is where natural selection has led two species to evolve one or more similar features.

Tends to occur when two species live in similar environments and have a similar lifestyle


where species evolve together in a reciprocal response to selective pressures


where all members of a species have died

background extinctions

the average rate of natural loss of a species

could be caused by changes to physical environment or changes in the ecological interactions between species

mass extinctions

large scale extinctions due to massive disruptive changes to the environment

molecular homology

-comparing morphological similarities can be useful in determining homology

-however, in the case of analogous features, it can sometimes be misleading (some organisms show what seem to be morphological similarities and yet do not share a recent ancestor)

-can be done w DNA and amino acid

Molecular homology w/ DNA

-all living organisms pass their genetic code to the next generation using DNA

-if all organisms shared a common ancestor, then as organisms diverge from other another, their genetic code/DNA should diverge with it due to different mutations over time

-by determining the number of nucleotide differences between the DNA sequences of two species, we can determine how closely related they are

Molecular homology w/ amino acid

-as differences accumulate in the DNA sequence, this can cause differences in the amino acid sequence

-hence, the amino acid sequence can be compared to determine homology

-the greater the difference, the less related the species are

Amino acid subsitutions can be..

conservative: the substitution amino acid has similar chemical property

semi-conservative - similar size amino acid but different chemical property

non-conservative: has a different size and chemical property

Molecular clocks

A molecular clock is a technique that uses the rate of accumulation of mutations in DNA to calculate how long ago organisms diverged from one another.

This hypothesis states that changes in DNA and proteins are constant over evolutionary time and across different lineages.

The change in DNA over time is also known as the mutation rate and can be expressed as the number of nucleotide changes that occur every million years.

The molecular clock hypothesis can be applied by calculating the rate of mutation of a region of DNA, along with the number of differences between the DNA of two organisms, and using this information to estimate how long ago they diverged.

Limitations of the molecular clock

One of its major limitations is the assumption that the rate of genetic change is constant and therefore accurately represents evolutionary time.

In order for genetic changes to occur at a constant rate, those changes need to be neutral or not affected by natural selection. This needs to be considered when applying a molecular clock to genetic data.

Any DNA regions that code for the phenotype of the organism are under natural selection and will change according to outside selection pressures. Therefore, the mutation rate of proteins and protein-coding DNA will not be constant.

The molecular clock is also limited when looking at very recent or ancient timescales.

When looking at recent timescales, it is less likely that enough time has passed to generate evolutionarily meaningful fixed differences in the sequences of different populations.

Instead, alternative alleles that may be present in both populations will lead to an overestimation of evolutionary distance.

Mitochondrial DNA (mtdna)

Genetic material is not just found in the nucleus of a cell. Mitochondria found in eukaryotic cells have their own genome.

MtDNA is unique in that it is passed through the maternal line of sexually reproducing organisms.

Mutations in mtDNA accumulate over time as they do in nuclear DNA. However, because mtDNA does not have the same repair mechanisms, the rate of mutation is higher than in nuclear DNA.

For this reason, mtDNA can be used as a molecular clock in relatively closely related species, while nuclear DNA is used to compare older lineages.

An added advantage of mtDNA is that it is easier to obtain high yields of DNA as most cells contain many mitochondria.

Techniques for measuring genetic differences: DNA hybridisation

DNA hybridisation is a technique that can be used to determine the level of similarity between sections of DNA of two species.

When a small section of double-stranded DNA is heated gently, the hydrogen bonds between complementary bases break and the two strands separate.

As the two stands are cooled, the complementary bases match up again and the DNA becomes double stranded once more.

If DNA from two organisms is gently heated to obtain single strands, mixed and then cooled, sections with similar nucleotide sequences will form hybrid double-stranded DNA.

-the amount of hybridisation is then measured to determine how closely related the species are

Rapid evolution

evolution is not always a slow process

it can occur in a short time resulting in rapid speciation

can occur when a relatively few mutations occur in master regulatory genes

Master regulatory genes

genes that control correct embryonic development

affect downstream structural genes directly or indirectly by controlling other regulatory genes

can influence multiple genes and hence multiple characteristics, causing major phenotypic changes

Changes in rate and timing (heterochrony)

causes the expression of a gene to slow or to become more active

this can lead to structural changes as one may grow faster or slower

Changes in spatial patterns

Determinesthe positioning of where the segments of the body grows.

Hox gene caused legsto grow rather than antennas.

Cichlid fish in East Africa

-subject to allopatric speciation due to flooding and droughts, causing adaptive radiation.

-jaws were found to differ between species as a result of BMP4, a heterochronic master regulatory gene which regulated the develop of cartilage and muscle cells

-fish with high levels of BMP4 present during development have heavy jaws with strong muscles, and lower levels have longer and more slender jaws.

The evolutionary process for the Cichlid fish

a single/few mutations in BMP4 gene (causing variation)


migration of fish due to flooding/drought


different selective pressures


survival of fish with most appropriate jaw type, will be passed on to next generation


eventual speciation

Darwin's Finches

-found on different islands in the Galapagos with different conditions, making them vary greatly in the size of their beak.

-high levels of BMP4 caused wide deep breaks to develop, while low levels caused slender beaks

-CaM protein regulates the activity of transcription enzymes by binding to them, changing the rate at which other genes are expressed, causing the beak length to vary

How are humans mammal?

-have body hair

-ability to suckle young

How are humans primates?

-grasping hand

-bicuspid teeth

-short nose

-well-developed eyes and brain

The Family Hominidae (Hominids)

-include the orangutan, gorilla, chimpanzee and humans

-features include: no tail, large body size, more complex cerebral cortex of the brain and an upper jaw

Distinguishing human features

bipedal: walk fully upright

-fewer, smaller teeth than apes

-flat face and lack heavy brow ridges

-large cranial capacity

-makes tools

-uses language and art

-is self-aware


Thegroup consisting of all modern and extinct Great Apes (that is, modern humans,chimpanzees, gorillas and orang-utans, plus all immediate ancestors)


Thegroup consisting of modern humans, extinct human species and all our immediateancestors (including members of the genera Homo)

Homo Sapiens: physical characteristics

-leaner, more agilebipedal structure

-high braincase

-flatter brow ridge

Homo Sapiens: behavioural characteristics

-higher levels ofcommunication and interaction

-abstract thinking


Homo Sapiens: cultural characteristics


-fire for cooking

-communal living invillages

-resource trading


Homo Floresiensis

They are one of themost recent additions to the human family tree

They coexisted withHomo Sapiens and were the most recent Homo species to become extinct.

It had a stature ofone metre tall, had a small brain and oversized teeth and feet.

They made andused some tools. And most likely used fire.

Homo denisovan

Denisovanswere closely related to humans and Neanderthals but genetically different.

Denisova cave and evidence from molecular suggests that interbreeding occurredbetween Denisovans and both these species.

Homo neanderthalensis

HomoNeanderthalensis is our closest extinct human relative.

They are different fromHomo Sapiens because they have larger faces with angled cheek bones, largenoses for coping with cold, dry air and chunkier, shorter builds suited tocolder climates.

Neanderthals did not use complex tools but they did use fireand lived with family groups in shelters.

It's thought they had complex socialstructures and were possibly the first human species to have language.

Theywere also the first species to wear clothes and jewellery, have burial ritualsand display symbolic behaviour.

Homo heidelbergensis

Theyare thought to be the first of the human species to use fire, the first tobuild shelters and the first to routinely hunt large animals.

Theyhas a very large brow ridge and a large braincase and was the first of theearly humans to successfully live in colder climates. Since their short, stockybuild was beneficial in conserving heat.

Homo erectus

Similar body proportions and behaviours to homo sapiens

First to construct tools using tools and other materials

Appeared to look after their sick, young and old.

First to cook food

Homo rudolfensis

Has a significantly larger brain case than the Homo Habilis which is how they differentiated between the two

Has a more elongated face and larger molar and premolar teeth resembling Australopithecines

Homo habilis

Much larger braincase than predecessors

Some of the first evidence of using stone tools, such as to access food

Had more ape like features than human, such as longer arms and jaws that project forward

Genus Paranthropus

Fossils of thegenus Paranthropus are characterised bytheir large teeth and powerful jaws.

- They were bipedaland stood around 1.3-1.4 m tall with a muscular build.

- were more specialised and less adaptable thanHomo species. This lack of adaptability in changing environments may have ledto their extinction

Genus Australopithecus

-skeletons show thatthey walked upright and climbed trees

-had both ape andhuman features, with a flat nose and curved fingers

Trends in human evolution

Brain case change

Prominent brow ridge

Longer legs

Pelvis modified

Shorter arms