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TOPIC 5: Evolution and Biodiversity, (Discuss how biochemical variations…
TOPIC 5: Evolution and Biodiversity
5.1: Evidence for Evolution
Evolution occurs when heritable characteristics of species change.
acquired traits cannot be inherited. evolution only concerns hertiable characteristics encoded in genes and transferred as alleles.
The fossil record provides evidence for evolution.
A fossil is the preserved remains or traces of any organism from the past.
preserved remains provide direct evidence of ancestral form
traces provide indirect evidence.
The totality of fossils is referred to as the fossil record.
Radioisotope dating
revealed the ages of the rock strata, and of the fossils in them, providing evidence that evolution has occurred.
evidence 1:
the sequence in which fossils appear matches the sequence in which they would be expected to evolve.
bacteria appear first and vertebrates last.
evidence 2:
the sequence fits with the ecology of the groups, where plant fossils come before animals.
evidence 3:
comparing an early homosapien ancestor that appears in the fossil record 4 million years ago to the bone structure of modern man shows evolutionary changes.
this ordered succession of fossils suggest that newer species evolved as a result of changes to ancestral species.
Selective breeding of domesticated animals shows that artificial selection can cause evolution.
artificial selection is when humans chose what animals should breed to express specific characteristics.
by continuously breeding members of a species with a desired trait, the
traits frequency becomes more common in successive generations.
selection can cause evolution as artificla selection has caused changes in the features of domisticated animals.
examples include dog breeding (hunting dongs bred to be smaller) or horse breeding for increased speed.
Discuss the incompleteness of the fossil record and the resulting uncertainties about human evolution. 4 marks
few fossils have been found;
most organisms decompose
only teeth and bones remain
require certain conditions for preservation
acids dissolve teeth/bones
there are many missing links (fossils of intermediate stages)
it is difficult to get conclusive evidence / difficult to falsify theories
Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function.
Homologous structure are anatomical features that are similar in structure but have different functions. Homologous structures have the same ancestral origin.
Adaptive radiation:
the rapid evolution of multiple species from a common ancestor/occurs when organisms with homo structures have all evolved from a common ancestor but have adapted to different environments in the process.
Analogous structures have a different ancestral origin, but they perform similar functions, evolved by convergent evolution.
convergent radiation:
Convergent evolution occurs when unrelated species develop similar traits or adaptations in response to analogous environmental pressures, despite not sharing a recent common ancestor.
Comparison of the pentadactyl limb of mammals, birds, amphibians, and reptiles with different methods of locomotion.
an example of a homologous structure is the pentadactyl limb in a variety of animals.
Despite possessing similar bone arrangements, animal limbs may be highly dissimilar according to the mode of locomotion:
crocodiles (reptiles) use their limbs for swimming
Bird and bat wings are adapted for flying
frogs (amphibian) use it for walking
Dolphin (mammal) fins are adapted for swimming
these have similar arrangements of bones in their 5-digit limb but use it for different functions.
Populations of a species can gradually diverge into separate species by evolution.
If two species become separated and do not interbreed, natural selection will act differently on the two populations and these will evolve in different ways.
The characteristics of the two populations while gradually diverge until forming separate species, resulting in infertile offspring in cross-breeding.
speciation is the formation of a new species by the splitting of a pre-existing species
Continuous variation across the geographical range of related populations matches the concept of gradual divergence.
populations located in close proximity that separated recently will show less divergence than populations that diverged a long time ago and/or are further away from each other.
over time, the two populations will adapt to different environmental conditions and gradually diverge from one another.
the degree of divergence between geographical separated populations will gradually increase the longer they are separated.
Development of melanistic insects in polluted areas.
insects that are melanistic are dark-colored. an insect with a melanistic variety is the
peppered moth
. this moth shows natural selection has occured as the melanistic variety became more common in polluted environments for better camouflage.
in an unpolluted environment pale colored lichen would be present.
the frequency of the two types of moth depends on the environment.
5.2: Natural selection
Natural selection can only occur if there is variation among members of the same species.
Better adapted organisms to the environment survive and reproduce, passing on their favourable alleles to their offspring.
nat selec. def = The process by which organisms that are better adapted to their environment survive, reproduce, and pass on their advantageous alleles, causing advantageous characteristics to increase in frequency within a population.
natural selection requires variation among members of the same species in order to differntiate survival (if all organisms were the same, we could not favor one over the other).
Over generations, the characteristics of the population gradually change due to evolution by natural selection.
natural selection can occur due to (1) inherited variation/genetic mutations (2) adaptations (3) competition (4) environmental pressures (5) genotypic frequency (6) evolution
ICE AGE
Describe how variation contributes to evolution by natural selection.
a. (variation is) different phenotypes/differences between individuals in a population/species*
b. struggle/competition for survival
c. some individuals have advantageous characteristics/are better adapted/have greater chance of survival/reproduction (than others)
d. favourable alleles/genetic variations passed on/inherited by offspring/next generation
Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
1)
mutations
produce new alleles which is an original source of genetic variation. new alleles by mutations enlarge the gene pool of a population.
2)
meiosis
produces new combinations of alleles by crossing over and exchaning alleles (DNA segements) between non-sister chromatids = resulting in recombinant chromosomes that have gene combinations that are not found in either parent cell.
random orientation of bivalents in meiosis increases genetic variation.
3)
sexual reproduction
involves the fusion of male and female gametes into the formation of a diploid zygote. meiosis results in genetically different gametes, so random fertilisation will generate different zygotes.
Adaptations are characteristics that make an individual suited to its environment and way of life.
adaptations (are charact...). adaptations develop by natural selection and they do not develop over the lifetime of an organism. acquired traits cannot be inherited.
Species tend to produce more offspring than the environment can support.
leading to a competition for survival + struggle for survival
A stable population will always outgrow its resources leading to competition for survival and an increased mortality rate.
darwin stated that living organisms will produce mnore offpsring than the environment can support and this will result in a struggle for survival and competition for resoruces.
Sea turtles can lay between 70 to 190 eggs, though only about one out of 100 typically survive
Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring.
The characteristics an offspring inherits could make them less or more well adapted to their environment, those that are less adapted tend to die or fail to reproduce.
variation in a population is determined by the presence of alleles.
beneficial alleles will make an organism better adapted/suited to their environment while
detrimental alleles will harm organisms chance of survival.
Individuals that reproduce pass on characteristics to their offspring.
the variation between individuals can be passed on to offspring - variation in behavior is heritable.
features acquired over time are not inherited =.
acquired traits are insignificant to the evolution of a species
Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species.
better adapted individuals tend to survive, and therefore they can reproduce to pass on their characteristics/favourable alleles to their offspring.
Less well adapted individuals have lower survival rates and less reproductive success.
over generations the characteristics of a population gradually change due to evolution by natural selection.
Changes in beaks of finches on Daphne Major.
an example of adaptive radiation (the rapid evolution of multiple species from a single species) by natural selection is seen in the variety of sizes and beaks of the finches in the Galápagos Islands.
darwin visited the galapagos islands to collect specimens of birds.
FINDING: variation in the shape and size of the beaks is due to different genes
darwins finches in Daphne major (island of galapagos) demonstrate adaptive radiation and variation in beak type and size according to diet.
(a drought changed the frequency of larger beak sizes within the population due to natural selection = dry conditions = plants produce larger seeds = finches with larger beaks were better adapted and surived and reproduced, passing on the advantegous allele to their offspring).
Outline one modern example of observed evolution by natural selection. 3 marks
beaks of Galapagos finches
competition for food
change in numbers/proportion of birds with different sized beaks
Evolution of antibiotic resistance in bacteria.
antibiotic resistance is due to genes in bacteria and so it can be inherited,
antibiotic resistant gene formed by mutation in one bacteria.
the evolution of antibiotic resistant genes in bacteria has been very quick because
(1) there has been a widespread use of antibiotics for treating disease in humans AND animals.
(2) bacteria reproduce very rapidly
(3) populations of bacteria are usually very large
(4) bacteria can exhange genes in plasmids by bacterial conjugation.
after an antibiotic is introduced --> bacteria with resistance will appear within a few years --> resistance to the antibiotic spreads to more species by evolution.
Outline what is required for speciation to occur.
a. divided species/gene pool / part of species/gene pool becomes separated / species splits into separate populations
b. reproductive isolation / lack of interbreeding
c. may be due temporal/behavioural/geographic isolation
d. different natural selection/different selective pressures
5.3: Classification and Biodiversity
The binomial system of names for species is universal among biologists and has been agreed and developed at a series of congresses.
the binomial system of nomenclature is the forrmal system by which all living species are classified.
the system allows for the identification and comparison of organisms based on recognised characteristics.
the binomial system of nomenclature shows how closely linked/related organisms are.
when specires are discovered they are given scientific names using the binomial system
the genus name begins with an upper case letter and the species name with a lower case letter = homo sapiens (sapiens is the species name, homo genus)
All organisms are classified into three domains.
The three domains of life are Archaea, Bacteria, and Eukarya.
eukarya contain membrane-bound nucleus
archae lack a nucleus and are found in ocean sediment
bacteria consist of common pathogenic forms
HISTONES = absent in bacteria, present in archae and eukaryota
INTRONS = absent in bacteria, present in some archae, present in eukaryota
CELL WAL = peptidoglycan (bacteria), archae have, some eukaryota dont
CELL MEMBRANE = present in all
The principal taxa for classifying eukaryotes are kingdom, phylum, class, order, family, genus and species.
KATY PERRY COMES OVER FOR GRAPE SODA.
organisms are grouped according to a series of hierarchical taxa.
Classification of one plant and one animal species from domain to species level.
Kingdom = ANIMAL (animalia) PLANT (plantae)
Phylum = ANIMAL (chordata) PLANT (angiospermophyta)
Class = ANIMAL (mammalia) PLANT (eudiocotidae)
Order = ANIMAL (primate) PLANT (ramucuares)
Family = ANIMAL (hominidae) PLANT (ramucuares)
Genus = ANIMAL (homo) PLANT (acris)
Species = ANIMAL (sapiens) PLANT (buttercup)
In a natural classification, the genus and accompanying higher taxa consist of all the species that have evolved from one common ancestral species.
All members of a genus or higher taxa should have a common ancestor. Because of the common ancestry we can expect the members of natural group to share many characteristics.
Artificial classification
involves randomly selecting unifying characteristics first and then grouping organisms accordingly, based on non-evolutionary features.
Natural classification
involves grouping organisms based on similarities first and then identifying shared characteristics.
Natural classification helps in identification of species and allows the prediction of characteristics shared by species within a group.
advantages of natural classification=
a. «because» it allows easier identification of a species
b. «because» it can help identify common ancestors/evolutionary paths/close relationships (showing degree of biodiversity) / OWTTE
c. «because» it is universal/
cons = highly mutuable so they tend to change as new information is discovered.
advantages of artificial selection = relatively stable and easy to develop
cons = does not show evolutionary relationships
Taxonomists sometimes reclassify groups of species when new evidence shows that a previous taxon contains species that have evolved from different ancestral species.
sometimes new evidence shows that members of a group do not share a common ancestor, so the group should be split up into two or more taxa.
species classified in differnt taxa are united if they appear to be closely related. so different species may be grouped into a shared taxon if new evidence suggest nmore recent common ancestors.
the Hominane sub-family was created to include gorillas and chimpanzees when it was found that they share common ancestry with humans
Construction of dichotomous keys for use in identifying specimens
A dichotomous key is a method of identification
whereby groups of organisms are divided into two catergoires repeatdely.
two types: description pair or flowchart
Recognition features of bryophyte, filicinophyta, coniferophyta, and angiospermophyta.
plants are classified together in one kingdom, and different plants are classified into different phyla.
BFCA (before fucking call angio). common= roots/leaves/spores/vascular/seeds
bryophyta have no roots
bryophyta have simple leaves
bryophyta produce spores ;
byrophyta are nonvascular;
filicinophyta have roots, stems and leaves;
filicinophyta produce spores on the undersides of leaves;
filicinophyta have primitive vascular tissue
coniferophyta have woody stems;
coniferophyta have narrow leaves;
coniferophyta produce seeds in cones/unenclosed seeds;
angiospermophyta have flowers;
angiospermophyta have ovules in ovaries;
angiospermophyta produce seeds (with hard coats) in fruits;
Recognition features of porifera, cnidarian pletyhelmintha, annelida, Mollusca, arthropda and chordata.
PCP MAA (mouth/anus --> symmetry --> skeleton)
porifera: no mouth and anus
porifera: no symmetry
porifera: internal spicules
cnidaria: mouth only
cnidaria: radial symmetry
cnidaria: soft skeleton
platyhelminthes: mouth only
platyhelminthes: bilateral symmetry
platyhelminthes: soft no skeleton
mollusca: moth and anus
mollusca: bilateral symmetry
mollusca: caco3 shell
annelida: mouth and anus
annelida: bilateral symmetry
annelida: internal cavity
arthropoda: mouth and anus
arthropoda: bilateral symmetry
arthropoda: external skeleton
Recognition of features of birds, mammals, amphibians, reptiles and fish.
FARBM (scale/skin: lungs: limbs:legs:reproduction)
fish: scales; gills; no limbs: fins: external fertilisation
amphibians: soft skin moist: lungs: tetrapod: 4 legs; external fertilisation
reptiles: imperable skin, lungs, tetrapod, 4 legs, internal fertilisation
birds: feathred covered: lungs: tetrapod: 2 legs 2 wings: internal fert
mammals: skin with follicles: lungs: tetrapod: 4 legs: internal fert
5.4: Cladistics
A clade is a group of organisms that have evolved from a common ancestor.
Species can evolve over time and split to form new species.
cladistics is a method of classifying organisms into groups of species called clades.
Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.
The genetic code is almost universal, so the base sequence can be compared.
Species that have a recent common ancestor can be expected to have a few differences in amino acid sequence.
Species that might look similar but diverged from a common ancestor millions of years ago are likely to have many differences in their base sequence due to natural selection and mutations.
the number of differences between comparable base sequences demonstrates the degree of evolutionary divergence
. A greater base sequence differences suggests more time has spent since two species diverged.
AMINO ACID SEQEUNCES are used to compare distantly related species
BASE SEQUENCE used to compare closely related organisms.
Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor.
differences in the base sequence of DNA and amino acid sequence of proteins are the result of mutations. they accumulate over time.
there is evidence that mutations occur at a roughly constant rate so they can be used as a molecular clock.
the number of differences in sequence can be used to deduce how long ago different groups split from a common ancestor.
Traits can be analogous or homologous:
homologous structures have a similar structure because they share a common ancestor (adaptive radiation)
analogous structures are similar in function because of convergent evolutios.
morphology is no longer used to identify a clade.
evidence from base sequences is used instead.
Cladograms including humans and other primates.
Cladograms are tree diagrams that show the most probable sequence of divergence in clades
cladograms are based on similarities and differences between the species in a clade.
cladograms are based on amino acid/base sequences
branching points in a cladogram are called
nodes
: the node represents an ancestral species that split to form two or more species.
The closest relatives of humans are chimpanzees and bonobos. the entire genome of these species have been sequenced giving very strong evidence for the construction of a cladogram.
the pattern of branching in a cladogram is assumed to match the evolutionary origins of each species
. The sequence of splits at nodes is a sequence in which ancestors of existing clades diverged.
if two clades on a cladogram are linked at a node, they are relatively closely related.
if two species are only connected via a series of nodes they are less related.
Cladograms provide strong evidence for evolutionary findings, but they do not provide proof.
they are constructed under the assumption that the smallest possible number of mutations occured to account for current base sequence differences.
Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group of species.
the construction of cladograms and identification of clades is known as cladistics.
it is now clear from cladograms that traditional classification based on morphology does not always match the evolutionary orgins of a group of species.
as a result some groups are reclassified.
Reclassification of the figwort family using evidence from cladistics.
The classification of the figworts was based on observable traits
When DNA sequence analysis began, plant scientists discovered that the shared features of the figwort family were in fact analogous and not evidence of shared ancestry
Three chloroplast genes were analysed
It was discovered that the
original figwort family was not a true clade
The figworts were found to contain several separate plant families
New families were created; several genera were moved into other existing families
Discuss how biochemical variations can be used as an evolutionary clock. 5 marks
methods of using evolutionary clocks: 3 max
differences in nucleotide base sequences / DNA / amino acid sequences / proteins
accumulate gradually over time
differences accumulate at (roughly) predictable rates
therefore the number of differences can be used as a clock
to measure the time since two divergent groups shared a common ancestor
example; e.g. amino acid sequences in globin genes
problems with using evolutionary clocks: 2 max
however variations are partly due to mutations
which are unpredictable chance events
so there must be caution in interpreting data
establish a variety of molecular clocks for reliability
(Kingdom) Animalia
(Phylum) Chordata
(Sub-phylum) Vertebrata
(Class) Mammalia
(Order) Primata
(Family) Hominidae
(Genus) Homo
(Species) sapiens
