Evidence for evolution & Mechanisms Of Evolution

Question 1

evolution

Answer 1

is defined as the change in the genetic composition of a population during successive generations, which may result in the development of new species

Question 2

microevolution

Answer 2

is defined as the small-scale variation of allele frequencies within a species of population, in which the descendant is of the same taxonomic group as the ancestor
- in simple terms this means the small changes in gene frequency within a population

Question 3

macroevolution

Answer 3

is defined as the variation of allele frequencies at or above the level of species over geological time, resulting in the divergence of taxonomic groups, in which the descendant is in a different taxonomic group to the ancestor
- this means big changes over long periods of time, causing speciation

Question 4

evidence for evolution comes from many different areas of biology:

Answer 4

• anatomy: species may share similar physical features because the feature was present in a common ancestor (homologous structures)
• comparative genomics: DNA and the genetic code reflect the shared ancestry of life. DNA comparisons can show how related species are
• biogeography: the global distribution of organisms and the unique features of island species reflect evolution and geological change
• fossils: fossils document the existences of non-extinct past species that are related to present day species
• direct observations: we can directly observe small-scale evolution in organisms with short lifecycles (e.g. pesticide-resistant insects)

Question 5

geological time

Answer 5

• evolution has occurred over very vast stretches of time
• geological time can be expressed in millions of years ago (mya)
• life on earth existed for 3.5 billion years
  Eon -> Era -> Period -> Epoch

Question 6

continental drift

Answer 6

• over time, the tectonic plates have moved significantly
• the fossil record can attest to this, and the current biogeography is explained by continental drift

Question 7

biogeography

Answer 7

• the study of the distribution of organisms and ecosystems across the world and through geological time
• the geographical distribution of species provides evidence that now isolated locations were once close
• the differences between species in different locations can give an indication of how much time has passed since they were co-located

Question 8

evolution and continental drift

Answer 8

• biogeography provides evidence for evolution
• for instance, most of the mammal species in Australia are marsupials (carry young in a pouch), while most mammal species elsewhere in the world are placental (nourish young through a placenta)
• Australia’s marsupial species are very diverse and fill a wide range of ecological roles
• because Australia was isolated by water for millions of years, these species were able to evolve without competition from (or exchange with) mammal species elsewhere in the world

Question 9

fossils

Answer 9

• fossils are the trace of a previously living organism
• for example, hard parts such as teeth, bones and shells but also include impressions left after soft tissue has decayed, or footprints, leaves, burrows or preserves faeces (coprolites)
• different types of fossils can tell us how organisms looked and moved, what they ate, how they reproduced and how they lived

Question 10

types of fossils

Answer 10

• moulds - imprint left by organisms with rock around it
• casts - imprint has been filled with rock
• body fossils - trapped in a substance or skeleton/hard body structures
• trace fossils - indirect evidence like footprints, burrows of faeces

Question 11

fossilisation

Answer 11

• fossilisation is a rare process and very few organisms are preserved in the fossil record
• fossilisation one absence of oxygen
• in some situations, the hard parts of organisms (natural bone or shell material) are replaced with minerals. This is mineralisation and makes fossilisation more likely
• organisms can be covered with sediment such as silt or sand. This can protect the remains from scavengers and slow the decay long enough for fossilisation to occur

Question 12

fossilisation requires:

Answer 12

• rapid burial of the material (this will ensure conditions are not suitable for the activity of decay organisms)
• presence of hard body parts
• long period of stability - the organism needs to be left undisturbed
• alkaline soil so that the minerals in the bones are not dissolved

Question 13

relative dating

Answer 13

used to determine the age of a rock, fossil contained in the rock, relative to other rocks or fossils found nearby
- strata are deposited in a time sequence, with the oldest on the bottom and the youngest on the top (principle of superposition)
- Palaeontologists can assign relative ages to fossils based on the strata in which they are found

Question 14

absolute dating

Answer 14

assigns a numerical age in years to a fossil or rock
- three main types: radiometric dating, electron spin resonance and luminescence
- most common methods of absolute dating is radioactive dating, which uses the known rates of decay of naturally occuring radioactive isotopes present in a rock or fossil

Question 15

law of fossil succession

Answer 15

• fossils can be dated by determining the age of the rock layer (strata) in which the fossil is found
• sedimentary rock layers develop in a chronological order, such that lower layers are older and newer strata form on top. This is called the principle of superposition
• each strata represents a variable length of time that is classified according to a geological time scale (eons, eras, periods)
• different kinds of organisms are found in rocks of particular ages in a consistent order, indicating a sequence of development
  – prokaryotes appear in the fossil record before eukaryotes
  – ferns appear in the fossil record before flowering plants
  – invertebrates appear in the fossil record before vertebrate species

Question 16

the principle of superposition

Answer 16

the principle of superposition indicates that the oldest rock layer is found at the bottom of the rock, with each consecutive layer above being relatively younger

Question 17

fossil records

Answer 17

evidence for early forms of life comes from fossils
- by studying fossils, scientists can learn how much (or how little) organisms have changed as life developed on Earth
- there are gaps in the fossil record because many early forms of life were soft-bodies, which means that they have left traces behind. What traces there were may have been destroyed of geological activity. This is why scientists cannot be certain about how life began
- fossils provide a snap shot of the past and allow us to study how much or how little organisms have changed as life developed on Earth

Question 18

transitional fossils

Answer 18

• show characteristics of both ancestral and descendant groups, showing a mid point in the evolutionary process
• transitional fossils demonstrate the intermediary forms that occurs over the evolutionary pathway taken by a single genus
• they establish the links between species by exhibiting traits common to both an ancestor and its predicted descendants
• an example of a transitional fossil is archaeopteryx, which links the evolutionary patterns are emerging and old assumptions are challenged

Question 19

the fossil record is incomplete

Answer 19

• the process of fossilisation requires very specific, and rare, conditions. The remains of the vast majority of long-extinct animals may never be found
• consequently, the fossil record is incomplete and biased toward organisms that lend themselves more easily to the fossilisation process

Question 20

comparative anatomy and embryology

Answer 20

comparative anatomy is the study of the similarities and differences in structure between organisms. Structural features are also called morphological features
- used to establish evolutionary relationships on the basis of structural similarities and differences, including the comparative study of embryos (embryology)
- longer they look the same - the closer related they are

Question 21

homologous structures

Answer 21

anatomical structures that are common to more than one species and were inherited from a common ancestor, but have different functions
- show the same structural plan but perform different functions due to the different species living in different environments with different selective pressures (conditions)

Question 22

pentadactyl limb

Answer 22

5 limbs, same pattern of bones, different size and shape - function

Question 23

divergent evolution

Answer 23

• is a pattern of evolution in which differences between groups of organisms accumulate to a critical point that leads to speciation, the development of a new species
• this pattern is usually the result of the dispersal of a single species to different environments, that is, groups from the same species become isolated from one another, stopping gene flow
• the sub-populations are subjected that can perform functions specific to surviving their unique environment
• homologous structures indicate divergent evolution, because new species will have the same fundamental structural plan, but the structures may be used in different ways

Question 24

adaptive radiation - a type of divergent evolution

Answer 24

• the evolution of an ancestral species, which was adapted to a particular way of life, into many different species, each adapted to a a different habitat
• adaptive radiation involves rapid speciation, and is likely to occur after an extinction event that creates many vacant ecological niches or colonisation of a new area
• example: darwins finches in the galapagos islands - evolved beak shapes - according to what they ate

Question 25

analogous structures

Answer 25

analogous structures are features of organisms that have the same function but not the same basic structure

Question 26

convergent evolution

Answer 26

- a pattern that occurs when unrelated organisms evolve similar adaptations in response to their environment - often results as analogous structures: adaptations of very different types of structures are genetically relatively different, but their functionality is very similar

Question 27

vestigial homologous structures

Answer 27

- homologous structures from a common descent can eventually cease to have any functional use for an organism - the structure may not necessarily impede a particular adaptation of an organism, but at the same time the structure no longer serves a 'useful' purpose - vestigial structures can take a variety of forms, including bones, soft tissues, organs, cells, or molecules - vestigial organs are evident for evolution, because it is hypothesised that they were once present and functional in their ancestors - changes in the environment have rendered these organs redundant, so over time they have lost their functionality - they demonstrate the evolutionary divergence of a species from a past behaviour or activity

Question 28

genomics

Answer 28

is the study of the whole set of genes of a species and the interactions of the genes within a genome. The genomes of many species have been fully sequenced. Complete genomes if many species have been fully sequenced. Complete genomes are now available for humans, chimpanzees, koalas and bacteria, among others

Question 29

relatedness

Answer 29

is a measure of evolutionary distance. The relatedness of groups of organisms is reflected in the similarity of their DNA sequences. Two species are more related if they have a more recent common ancestor and less related if they have less recent ancestor

Question 30

comparative genomics

Answer 30

is a field of biological research in which researchers use a variety of tools to compare the genome sequences of different species. The more similar in sequence the genes and genomes of two species are, the more closely related those species are

Question 31

biological classification

Answer 31

is the categorisation of living organisms into similar groups according to certain criteria. - involves the organisation of living organisms into similar groups according to certain criteria. These groupings used to rely on morphological characteristics: organisms that had similar features were assumed to be closely related. Unfortunately, using only morphological characteristics to infer species relatedness got tricky in cases of convergent evolution - Its a method of organising the millions of species on Earth in a meaningful way that helps scientists to understand certain evolutionary relationships between them - it involves describing and naming different organisms, then organising these species into a group with other, closely related species - grouping species makes it easier to see information about them and provides a system in which species can be classified in a predictable way

Question 32

species definition

Answer 32

a group of similar organisms that are capable of interbreeding to produce viable, fertile offspring

Question 33

how is biological classification helpful

Answer 33

- it helps determine how closely related different organisms are, and when they last shared a common ancestor

Question 34

convergent evolution

Answer 34

is where species that aren't closely related have evolved similiar traits due to similar selection pressures within their environment. if we were to rely on morphological characteristics to determine the degree of relatedness between these species, we would likely think they were more closely related than they truly were

Question 35

DNA hybridisation and - species relatedness

Answer 35

- provides a way to compare genomes of different species by measuring the degree of genetic similarity between DNA sequences - the more similar the DNA sequences of two species are the more closely related the two species are

Question 36

DNA hybridisation steps

Answer 36

1. DNA from the two species to be compared is extracted, purified and cut into short fragments 2. the DNA of one species is mixed with the DNA of another 3. the mixture is incubated to allow DNA strands to dissociate and reanneal, forming hybrid double stranded DNA 4. the hybridised sequences that are highly similar will bind more firmly 5. a measure of the heat energy required to separate the hybrid strands provides a measure of DNA relatedness - the lower the temperature that is required to split the hybrid strands of DNA compared to the DNA of the original species the less similar the species are

Question 37

DNA sequencing

Answer 37

- was a time-consuming and expensive process right up until the 1970's, when scientist Frederick Sanger developed faster, more efficient techniques. This was called the Sanger sequencing process and gave a platform for other, more refined techniques to also be developed - now, modern DNA sequencing allows for a direct comparison of the exact sequenced of the four bases that make up an organisms DNA. In contrast, hybridisation can only estimate the differences between the DNA of different species - this means that scientists can determine the exact number of similarities or differences between the DNA sequence of two different species. More closely related species will show more similarities in their base sequences

Question 38

Sanger definition - DNA sequencing

Answer 38

the discovery of the Sanger sequencing process was enough to earn Sanger himself a noble prize in 1980. This technique is still used today, but other ones have been developed that take even less time and cost less as well. These include pyrosequencing and nanopore sequencing

Question 39

DNA sequencing - species relatedness

Answer 39

- if two organisms share the same DNA sequences, then we can say that they are the same species. If they had only a small number of differences in the order of the bases, then we can say they are closely related - if the two organisms had a large number of differences in the order of the bases in the DNA sequences, then we can say they are distantly related. Their last common ancestor would have existed tens, if not hundreds, of millions of years ago

Question 40

Amino acid sequencing

Answer 40

- amino acid sequences form larger molecules called proteins - as species accumulate mutations the sequence of the amino acids that form proteins will change - as such we can isolate a particular protein (often called a ubiquitous protein) that we know is found in multiple different species. We can then compare the amino acid sequence for each species that results ultimately in the formation of the same protein - if two species share a recent common ancestor, then they will be closely related and the respective amino acid sequence for the chosen protein will be very similar

Question 41

Cytochrome C

Answer 41

- is an example of an ubiquitous protein - Human Cytochrome C has 104 amino acids - 27 of the amino acids in Cytochrome C are found in every molecule sequenced, from bacteria to humans - performs essential step in cellular energy production - has changes little over millions of years of evolution - strong evidence that the genes for Cytochrome C production originated from a primitive microbe ancestor, more than 2000 million years ago - Cytochrome C of chimpanzees, gorillas and humans is identical

Question 42

Bioinformatics

Answer 42

- is the digital storage, retrieval, organisation and analysis of an enormous volume of biological data - Bioinformatics has dramatically increased the size, accuracy and scope of data sets, such as those needed for comparative genomics - bioinformatics has provided significant advances in our knowledge of the entire genomes of organisms, and in turn this has revealed yet more evidence of evolution

Question 43

Phylogenetic trees

Answer 43

- evolutionary relationships between groups can be represented using phylogenetic trees - these diagrams show how organisms are related to each other, but the tree is a hypothesis, not a certain fact - a phylogenetic tree can be built using: -- physical information, such as body shape, bone structure or behaviour -- molecular information, such as genetic sequences - essentially the species that are considered more closely related (they might share key morphological characteristics and have similar sequences of amino acids of DNA) will be grouped into clades

Question 44

parts of a phylogenetic tree

Answer 44

- root - node - outgroup - clade - taxon

Question 45

root

Answer 45

initial ancestor

Question 46

node

Answer 46

hypothetical common ancestor where branching occurs

Question 47

outgroup

Answer 47

most distantly related species

Question 48

clade

Answer 48

a group of organisms that include a common ancestor and all its descendants

Question 49

taxon

Answer 49

a group of organisms (can refer to any rank; species, genus, family, etc)

Question 50

phylogenetic trees construction

Answer 50

remember, when looking at a phylogenetic tree, we are most interested in the positions of the nodes and grouping of branches as this represents the evolution of taxa. While all four different tree types (horizontal, vertical, diagonal and square) look different, it is important to realise that one set of data represented by each different type of trees will always depict the same evolutionary relationships

Question 51

phylogeny

Answer 51

explains similarities and differences between organisms establishes relationships between groups

Question 52

mechanisms for evolution

Answer 52

1. mutations 2. natural selection 3. genetic drift 4. gene flow (migration)

Question 53

mechanism for evolution - mutation

Answer 53

- a permanent change in the DNA sequence of a gene - changes the frequency of alleles in a population - introduces new alleles not present before - creating variation in DNA sequences that result in different phenotypes - new alleles can be beneficial, harmful or neutral - harmful (deleterious) mutations will reduce in frequency (e.g. Cystic fibrosis) - beneficial mutations will spread and become more common (e.g. dark peppered moth, antibiotic resistance in bacteria, longer necks in Galapagos tortoises) - leading to evolution - a mutation causes a new allele in the gene pool - the frequency that each occurs changes depending on "fitness" - this is the organisms ability to survive and reproduce

Question 54

theory of evolution

Answer 54

- explanation for the huge diversity of life on Earth - underpinned by comprehensive evidence - initially put forward in 1858 by: -- Charles Darwin -- Alfred Russel Wallace - allowed him to observe differences and similarities between geographically separated animals - theory based on 3 observations made by Darwin

Question 55

Charles Darwin

Answer 55

- keen amateur naturalist - joined a surveying expedition as a biologist - voyaged on HMS Beagles -- Galapagos Islands -- New Zealand -- Australia

Question 56

Darwins 3 observartions

Answer 56

- variation: members of a species vary and variations are passed on from one generation to the next - birth rate: living organisms reproduce at a rate greater than their food supply and must compete for resources - natures balance: although birth rate is high, most species numbers remain at a constant level based on the observations, Darwin interpreted and inferred: - excessive birth rate and limited resources -> struggle for existence - variations mean the organisms best suited to their environment are more likely to survive -> become known as "survival of the fittest" -- more organisms with favourable characteristics survive -- organisms with less favourable characteristics die before they can reproduce -- survival of fittest possible because of variation

Question 57

mechanism for evolution - natural selection

Answer 57

occurs when -- selection pressures in the environment -- give an advantage to a specific phenotype -- increases its survival and reproduction - "survival of the fittest" - when individuals in a population possess certain traits/alleles that allow them to survive selective pressure, reproduce and pass on the favourable alleles - an inherited trait that allows an individual to survive and reproduce is called an adaptation - natural selection only acts on inheritable traits - selecting for beneficial alleles and increasing their frequency, and selecting against deleterious alleles and decreasing their frequency - adaptative radiation

Question 58

selection pressures

Answer 58

- competition -- between species -- within species - predator-prey relationships - sexual selection - environmental factors - human impacts, climate change, pollution

Question 59

sexual selection

Answer 59

- selection by male/female individuals that assist in winning of a male or in copulation - type of natural selection linked to mating behaviour of animals - leads to dimorphisms (separate male/female)

Question 60

phenotypic selection

Answer 60

- selection of allele frequency in a gene pool can be positive or negative - as phenotype is largely determined by genotype, the genotype helps determine the reproductive success (fitness) of an organism - characteristics may be selected for (positive) or against (negative) depending on the environmental conditions. This will in turn affect the frequency of the alleles in the gene pool

Question 61

principles of natural selection

Answer 61

1. variation 2. overproduction 3. competition and survival of the fittest 4. reproductive rate is higher 5. heritability 6. change in allele frequency

Question 62

variation

Answer 62

- individuals in a population show variation/they differ from one another - variation is due to mutations in alleles, meiosis (crossing over, independent assortment and random segregation) and random fertilisation

Question 63

overproduction

Answer 63

- there are more individuals produced in a population than the environment can support - environmental resources such as food, water, shelter, reproductive partners are limited

Question 64

competition and survival of the fittest

Answer 64

- environmental factors such as food availability, predators, disease favour those with advantageous traits/alleles - those individuals with the advantageous trait/allele will outcompete those without the trait/allele

Question 65

higher reproductive rate

Answer 65

- those individuals with the advantageous allele are more likely to survive, reproduce and therefore have a higher reproductive rate

Question 66

heritability

Answer 66

- characteristics that assist survival/advantageous alleles are more likely to be passed down and inherited by the offspring

Question 67

allele frequencies change over generations

Answer 67

- over consecutive generations, the frequency of the advantageous allele increases and the disadvantages decreases - over many generations the advantageous allele can become fixed - 100% and the disadvantageous allele extinct - 0%

Question 68

peppered moths

Answer 68

- 2 forms exist - dark and light - dark forms easily caught by predators (birds) if they live on light coloured trees, light forms are more likely eaten if surroundings are dark - in unpolluted areas, trees are pale and the dark forms decrease - in polluted areas, trees are darkened will pollution and the pale forms decrease - in this case the selection pressure (predation) is affected by the colour of their surroundings

Question 69

antibiotic resistance in bacteria

Answer 69

- variation exists in the population - so some are more resistant to antibiotics than others - when there are treated, the resistant forms are more likely to survive - these will breed and pass on their resistant alleles to their offspring - after several generations, the population will consist of mainly resistant bacteria

Question 70

natural selection is:

Answer 70

- selective: it selects for a particular allele based on an organism's phenotype - directional - the allele frequencies change in the direction of the advantageous allele (it increases) - adaptive - it drives adaptation based on an environmental pressure

Question 71

the mechanism of adaptive evolution

Answer 71

- natural selection is driving force for adaptive evolution - natural selection is the only mechanism that can lead to adaptive evolution (new species that are better suited to their environment (adaptation))

Question 72

artificial selection

Answer 72

- also called selective breeding - the international breeding or reproduction by humans of individuals with desirable traits, resulting in changes of allele frequencies in gene pool over time - human intervention decides what traits are selected for, usually traits beneficial to humans - applied to agricultural species, pets - over many generations, the practise leads to the development of strains with the desired characteristics

Question 73

steps in selective breeding

Answer 73

1. choose parent organisms that show desired traits and breed them 2. choose the best offspring form these parents to breed the next generation 3. repeat the process across many generations. Over time, the desired traits will become more common

Question 74

examples of selective breeding

Answer 74

- intentionally mating 2 dogs in order to achieve or eliminate a specific trait - a farmer saves seed from a hearty crop to replant the next year - dogs are bred for competition or for hunting - cows can be bred to increase muscle mass or milk production - cabbage and cauliflower were developed from the wild mustard plant

Question 75

pros of selective breeding

Answer 75

- farmers can produce crops with higher yield - farmers can produce animals that grow more meat, more milk, more eggs, faster and stronger - can produce friendlier and prettier pets

Question 76

cons of selective breeding

Answer 76

loss of genes in a population - by not allowing some animals to breed, their genes could be lost forever in a population animal discomfort - may cause physical problems such as animals bred for rapid weight gain may develop muscular/skeletal problems - farmers breed cows to have large udders, so now since cows have difficulty walking and have health problems - some chickens are too heavy to stand, so they have to lay down all the time can lead to interbreeding - in order to create a certain type of animal through selective breeding, sometimes brothers and sisters of a population will mate to pass on favourable traits, and this can lead to health problems

Question 77

gene pools

Answer 77

- natural selection acts on alleles, which are inheritable - the total collection of alleles that exists within a population is called its gene pool

Question 78

population

Answer 78

is a group of individuals of the same species, which live in the same geographic area and readily interbreed to produce fertile offspring

Question 79

allele frequencies - how do they change in populations?

Answer 79

- unless there is an evolutionary process acting on a population, the allele frequency in the population's gene pool should remain the same from generation to generation - although the proportions of phenotypes in the population may change, the proportions of alleles in the gene pool should not - but real populations do not change over time and microevolutionary change does happen

Question 80

three processes that leads to change in populations?

Answer 80

- mutations of an allele, introducing a new allele to the gene pool - gene flow - immigration into the population and emigration out of the population - genetic drift

Question 81

variation created through mutations

Answer 81

- mutations of an existing allele can produce a new allele - alleles introduced this way are often recessive and stay hidden, unless individuals breed with related individuals - recessive alleles are often deleterious, but are also an important source of biological variation - mutation create variation within the gene pool or genetic diversity. Genetic diversity is what allows evolution to occur - this is because genetically diverse populations have a greater range of phenotypes which increases the chance that at least some individuals will survive in the face of environmental change

Question 82

gene flow

Answer 82

- migration is the movement of individuals between populations - when individuals move from one population to another and then breed with the residents of the new population, 'Gene flow' can change frequency of alleles in the new population - immigration - movement of individuals INTO a population - emigration - movement of individuals OUT OF a population migration does NOT create new genetic variation, it moves around already existing variation

Question 83

allele frequency

Answer 83

- allele frequency is simply how common an allele is in a population - consider a gene that has 2 alleles: A and a, the frequency can be worked out using the following: the frequency of allele A = number of A alleles in the population / total number of alleles in the population

Question 84

(random) genetic drift

Answer 84

- genetic drift occurs because alleles are inherited randomly from parents - it describes changes to the gene pool that occurs by chance and are not driven by selection pressures. These changes can occur: - because allele frequencies are not the same from generation to generation. for example, an allele may not be passes on to the next generation and, in small populations, this may mean that it is soon lost from the gene pool entirely - because a change event may kill individuals non-selectively, altering the allele frequencies in the gene pool - the effect of genetic drift are much easier to see in small populations - whereas the effects of genetic drift on large populations are minor compared to the entire gene pool and are often overshadowed by natural selection, genetic drift working in small populations can result in big changes

Question 85

there are two kinds of genetic drift

Answer 85

- founder effect - bottleneck effect

Question 86

the founder effect

Answer 86

- this occurs when a small number of individuals found a new population (they colonise a new isolated area such as an island) - the alleles present in the founding members of the new population may not be representative of the original population - due to the small population there is a greater chance for genetic drift to occur and there to be a lower range and frequency of alleles - as a result evolution is likely to occur faster in founder populations when compared to the original population

Question 87

the bottleneck effeect

Answer 87

- it occurs when a population is drastically reduced in size, for example by a natural disaster. The alleles present in the surviving members of the population may not be representative of the original population. The range of alleles will be reduced and the frequency of the alleles will change. If the population increases again, it will have a reduced genetic biodiversity - this makes the surviving population more at risk of extinction

Question 88

speciation

Answer 88

natural selection produces changes in the allele frequencies of gene pools when the changes become so great the populations are so different that they can no longer reproduce with one another - speciation has occured - natural selection causes microevolution within a gene pool - eventually a population accumulates enough changes that a new species can be identified and speciation has occurred - sometimes several speciation events occur and lead to a collection of new species or even higher classification groups. this is macroevolution - microevolutionary changes build up over time to produce macroevolution this occurs when populations are reproductively isolated. Because of this they are subjected to different selection pressures - these differing selection pressures mean that the population changes significantly from the original population to form a new species

Question 89

steps in speciation

Answer 89

1. variation - original population - one population, one species - within a population a range of variety of characteristics exist. this population shares a common gene pool 2. isolation - initial step of speciation - two populations, one species - a barrier has formes which prevents interbreeding between the two populations. the two populations now have separate gene pools 3. selection - evolution of reproductive isolation - two subspecies, one species - in each population, over a number of generations, different selection pressures will act to bring about a change in the gene frequencies of each gene pool. such a changing population is evolving into separate subspecies 4. speciation - new distinct species after equilibrium of new ranges - two species - if isolation and selection continue over a long period of time, the changes in the gene frequencies can become great enough to prevent population from ever interbreeding successfully. When this happens the populations have evolved into separate species the key in speciation is there must be isolation - gene flow must be inhibited between the two groups so natural selection can happen independently of each other

Question 90

isolated mechanisms

Answer 90

- isolating mechanisms separate two subgroups of a population and prevent them from producing fertile, viable offspring - these mechanisms can operate before reproduction has occurred or after reproduction - the organisms become so genetically diverse that they form two new species - they are then no longer able to interbreed, even if the populations come back together

Question 91

pre-reproductive/prezygotic isolating mechanisms

Answer 91

pre-reproductive isolating mechanisms are biological or ecological mechanisms that prevent organisms from being able to interact to reproduce: - geological from physical barriers: such as rivers, mountain ranges, oceans - temporal (time) mechanisms: individuals breed during different seasons of the year of times of the day - behavioural mechanisms: individuals have different seasons of the year of times of the day - morphological mechanisms: individuals have different reproductive structures

Question 92

post-reproductive isolating mechanisms

Answer 92

three mechanisms don't prevent mating but prevent formation of viable, fertile offspring - gametes mortality (gametes do not survive after mating) - zygote mortality (zygote forms but does not survive) - hybrid sterility (adult offspring develop but cannot produce viable gametes) - hybrid sterility is not often a reproductive isolating mechanism in plants, where polyploidy is common

Question 93

allopatric speciation

Answer 93

in allopatric speciation from the ancient Greek 'allos' = other and 'patro' = homeland, gene flow is disrupted when populations become physically separated through geographical isolation. The populations diverge. This may be become of different selection pressures acting on the two populations, or it may be due to other random processes such as genetic drift - allopatric speciation occurs as populations are geographically isolated

Question 94

allopatric speciation - physical barriers that can separate a subpopulation from its original population:

Answer 94

- water, for terrestrial organisms - land, for aquatic organisms - mountains

Question 95

allopatric speciation - new physical barriers can arise due, among other things, to:

Answer 95

- continental drift - rising sea levels - climate change

Question 96

steps in allopatric speciation

Answer 96

- subpopulations - isolated by physical barrier - no gene flow - different selection pressures - natural selection - two different species - genetic drift will occur independently in subpopulations

Question 97

case study: squirrels and the grand canyon

Answer 97

- before the grand canyon was carved out by the Colorado river, only one species of squirrel inhabited the area - as the canyon got deeper over time, it became increasingly difficult for squirrels to travel between the north and south sides - eventually it was too deep for the squirrels to cross, they became isolated on each side resulting in two sub-populations that were reproductively isolated from each other - eventually these populations became two species

Question 98

extinction

Answer 98

selection pressures can become so great that species become extinct

Question 99

causes of extinction

Answer 99

genetics and demographics - small populations = increased risk - mutations -- causes a flux in natural selection -- beneficial genetic traits are overruled - loss of genetic diversity -- shallow gene pools promote massive inbreeding - habitat destruction - natural causes (asteroids, acid rain, disease)

Question 100

mass extinction

Answer 100

extinction occurs quite rarely but there have been periods when the rate of extinction has been quite high. These are mass extinction we appear to be in the midst of the sixth mass extinction, which began around 50,000 years ago, when modern humans spread out of Africa this coincided with the extinction of several species of megafauna

Question 101

Australia bushfires and species extinction

Answer 101

more than 1 billion animals were killed in the 2019/2020 Australia bushfire season. Endangered species, including the long-footed potoroo, Kangaroo Islands gloss black cockatoo and Batman Bay's Spring midge orchid were pushed towards extinction the devastating wildfires undid decades of careful conservation work on Kangaroo Island and have threatened to wipe out some of the islands unique fauna altogether - preservation of genetic diversity is key to preventing extinction - having a large gene pool means having more alleles to draw upon to face the pressures of natural selection

Question 102

preventing extinction

Answer 102

- biogeography - involves maintaining population distributions and allowing populations to remain connected -- conservation areas -- wildlife corridors - reproductive behaviour - that maintains diversity and random mating practices - population dynamics - maintaining population size and density

Question 103

preventing extinction by preserving genetic diversity

Answer 103

populations with reduced diversity face increased risk of extinction, so conservation projects usually focus on maintaining genetic diversity rapid extinction events can lead to greater loss of large organisms than of small ones. A large distribution area is generally a big advantage, because it may allow some pockets of habitat to survive large population size can also be some protection, because the population is likely to have a more diverse gene pool and thus a greater variety of alleles and phenotype options as the pressures from natural selection change