Evolution and Biodiversity Flashcards
What does evolution mean?
The cumulative change in the heritable characteristics of a population over time. It involves a change over time in the allele frequency.
What is a gene pool?
All the genes and their alleles present in an interbreeding population
What is the frequency of an allele?
The number of that allele in a population divided by the total number of alleles of the gene. It is a measurement of the proportion of an allele in the population
Why may there be differences in allele frequency?
Due to differences in natural selection
Random/genetic shift
What is speciation?
The formation of new species by the splitting of a species into two/mpre
What is needed for speciation to take place?
A population should become reproductively isolated. This keeps the gene pools separate.
What happens if natural selection acts indifferently on the isolated population?
The allele frequency in its gene pool will change and it will gradually diverge. Eventually, the isolated population will be incapable of interbreeding- it has become a new species.
What is allopatric speciation?
The formation of new species by populations that become reproductively isolated due to geographical/physical separation. It occurs in different geographical areas
What is sympatric speciation?
The formation of new species by populations that inhabit the same or overlapping geographic regions and are reproductively isolated due to behavioural isolation, temporal isolation or polyploidy. Occurs in the same geographical area
What are the types of reproductive isolation?
Geographical, temporal isolation and behavioural isolation
What is geographic isolation?
When populations of a species live in different areas and therefore do not interbreed
What is behavioural isolation?
When populations of a species have behaviour that prevents interbreeding
What is temporal isolation?
When populations of a species breed at different seasons or times of the day.
What is polyploidy?
it is having more than two sets of homologous chromosomes
How can polyploidy result?
- If non-dysjunction occurs resulting in a diploid gamete. The diploid gamete when fused with a haploid gamete produces triploids, which are infertile because homologous chromosomes cannot pair up and meiosis fails.
- Tetraploid cells can also result of chromosomes duplicate in preparation for meiosis but then no meiosis occurs.
What can polyploidy cause?
Instant speciation and can lead to sympatric speciation.
Give an example of polyploidy
In the genus Allium, polyploidy has occurred frequently and has led to speciation. This has resulted in a number of reproductively isolated populations. Most Allium species have a diploid number that is a number of 16. The ancestral Allium probably had this number. Allium species with 32 chromosomes are tetraploids and evolved by polyploidy. Many species of Allium reproduce asexually and polyploidy can confer an advantage over diploidy under certain conditions.
adaptive radiation
The rapid evolutionary diversification of a single ancestral line into several new species
What is adaptive radiation?
When members evolve different morphological features due to the different selection pressures.
What are homologous structures?
Homologous structures are structures that have evolved from the same part of a common ancestor and are the result of adaptive radiation.
What are examples of adaptive radiation?
- Beak types of the finches of the Galapagos Islands
- Pentadactyl limb
What is convergent evolution?
The independent evolution of similar features in species where the similar feature is not inherited from the common ancestor.
How may convergent evolution happen?
May occur when different species occupy the same habitat and are thus subjected to the same selection pressures.
What does convergent evolution lead to?
To the evolution of analogous structures
What are homologous strucutres?
Structures in different species that may perform different functions, but have the same basic structure.
How do homologous structures arise?
They have originated from a common ancestor and they are a result of adaptive radiation.
What are the analogous structures?
They have separate evolutionary origins, but are superficially similar because they perform similar functions. They are the result of convergent evolution.
What are evidence supporting evolution?
Evidence from fossils
Evidence from selective breeding of domestic animals
Evidence of homologous structures
Evidence from patterns of variation
Biochemical evidence
What is evidence from fossils?
- fossils are the preserved remains or traces of an organism from the past
- rock layers on the Earth develop in a chronological order
- radioisotope dating reveals the age of rocks and of the fossils in them
- the sequence in which organisms appear in the fossil record matches their complexity and the expected sequence of evolution
- Comparisons between fossils and living organisms show that changes from an ancestral form have occurred over time in the characteristics of living organisms.
- Transitional fossils demonstrate intermediate stages in the evolution of groups and link together existing organisms with their likely ancestors.
- DNA can be taken from fossils for molecular clock analysis
What is evidence from selective breeding of domesticated animals?
- Selective breeding is a form of artificial selection where humans breed species to produce desired traits in the offspring
- The striking differences in the heritable characteristics between domesticated breeds show that species can evolve rapidly by artificial selection
What is the evidence from homologous structures?
Amphibians, reptiles, birds and mammals have limbs that serve different functions. However, the basic bone structure is the same. The structure is known as the pentadactyl limb and is an example of homologous structure. The most likely explanation is that all these vertebrates share a common ancestor with pentadactyl limbs. This is a type of evolution called adaptive radiation.
What is evidence from patterns of variation?
If populations gradually diverge and there is no sudden switch, one would expect to find examples of all stages of divergence at any moment. The continuous range in variation supports the origin of new species by evolution.
What is biochemical evidence for evolution?
All organisms have DNA as genetic material.
All organisms have 20 aa.
The genetic code is universal.
What is natural selection?
Natural selection can only occur if there is genetic variation between members of the same species. The theory was proposed by Charles Darwin.
How does natural selection work?
- Species produce more offspring than the environment can support
- This leads to a struggle for survival within a population: the individuals compete for resources- some individuals survive and some die
- Or there is an environmental change that exerts selection pressure
- individuals of a population show variation
- some individuals are better adapted than others
- The better adapted tend to survive and produce more offspring while the less well- adapted tend to die or produce less offspring
- Individuals that reproduce pass on the alleles to their offspring and so the frequency of alleles that make individuals better adapted increases the population’s gene pool
What is variation?
The differences between members of a species.
What are sources of variation?
Gene mutations
Meiosis
Sexual reproduction
What are adaptations?
Characteristics that make an individual suited to its environment and way of life and thus aid its survival
What are examples of evolution by natural selection?
- Antibiotic resistance
- Changes in beaks of finches on Daphne Major
- Industrial melanism
Describe how antibiotic resistance shows evolution by natural selection
A bacterium with antibiotic resistance appears randomly due to gene mutation and reproduces
- Variation is created within a population
- The antibiotic resistance gene can be transferred from bacteria by plasmid
- If an antibiotic is used the non-resistant bacteria are killed
- If there is no competition, so the antibiotic resistant bacteria survive and grow rapidly
- The more an antibiotic is used the more resistant bacteria there will be
How is a bacterial strain tested to see if it is resistant to an antibiotic?
The zone of inhibition method is used. In this the bacterial strain is spread on an agar plate with nutrients. Discs with antibiotic are placed on top. The antibiotic diffuses from the disc. If the bacteria are non-resistant they are killed by the antibiotic and a zone of no growth forms around the disc, called the zone of inhibition.
Describe how the changes in beaks of finches on Daphne Major show evolution by natural selection
The population of Geospiza fortis, which feeds on seeds which are either small or large. There is variation in the size of beaks with some individuals having larger beaks than others. During droughts there are few small soft seeds available but larger hard seeds were still produced. The mean beak size of the finches that died during the drought was smaller than the beak size of those that survived. This natural selection occurred because finches with large beaks are better adapted to eating larger seeds.
Describe how industrial melanism is an example of evolution by natural selection
There are two varieties of the peppered moth: a light-coloured and a melanistic variety. In unpolluted areas branches are covered with pale lichens. The light variety is well camouflaged from birds. The melanistic variety was very rare in these areas. When industry developed, the lichens died and soot from coal burning made the branches darker. The melanistic form could camouflage well in the dark branches, survived more and reproduced to pass on the alleles of dark colour.
What are the three types of selection?
Stabilizing selection
Disruptive selection
Directional selection
What is stabilizing selection?
Intermediates are selected for and both extremes are selected against
What is disruptive selection?
Both extremes are selected for and intermediates are selected against
What is directional selection?
One extreme in the range of variation is selected for, the other extreme is selected against. This causes the phenotypic distribution to shift in one direction
Describe gradualism
Evolution that occurs at a constant pace. It occurs when conditions are rather stable. Speciation occurs by a slow gradual divergence over a long time. There is a long sequence of continuous intermediate forms. Some fossil records have many intermediate forms connecting the ancestral species to the modern equivalent.
Describe punctuated equilibrium
There are long periods of relative stability and short periods of rapid evolution. Speciation is abrupt and happens suddenly. Events such as rapid environmental change can lead to rapid speciation. The gaps in the fossil record/ lack of intermediate forms supports this theory.
What is classification?
The process of putting species into groups
Why is classification important?
There is great biodiversity/huge number of species. It allows storing, accessing and communicating the information about species. It suggests the evolutionary relationships between organisms
What is artificial classification?
A characteristic is arbitrarily selected and organisms are put into groups depending on whether they have the characteristic or not. However, insects, birds and bats are not similar in enough ways. Even their wings have different structure bc they are not homologous. Artificial classification is not used because it does not show evolutionary relationships
What is natural classification?
In natural classification, the species in a group have evolved from a common ancestor. They share characteristics that they have inherited from this ancestral species.
Why is natural classification useful?
- Allows the prediction of characteristics shared by species within a group
- Allows easier identification of species
- Helps identify evolutionary paths
- Allows biodiversity research of larger taxa
List the hierarchy of taxa
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
What is the classification of humans?
Domain - Eukaryota
Kingdom -Animalia
Phylum - Chordata
Class - Mammalia
Order - Primates
Family - Hominidae
Genus - Homo
Species- Homo sapiens
What is the classification of date palm?
Domain - Eukaryota
Kingdom - Plantae
Phylum - Angiospermophyta
Class - Monocotyledonae
Order - Palmales
Family - Arecaceae
Genus - Phoenix
Species- Phoenix dactylifera
What is traditional classification?
It is based on comparative anatomy: species are put in a group based on shared anatomical/structural characterisitc
What is modern classification?
It is based on comparisons of base sequences of DNA or amino acid sequences of proteins: the more the similarities in the sequences, the more closely related the two species are
What are the problems of traditional classification?
- It is not easy to which groups of species share a common ancestor based on structural traits bc these traits might be analogous.
- Closely related organisms can exhibit very different structural features due to adaptive radiation.
- Distantly related organisms can display very similar structural features due to convergent evolution.
Describe how modern cladistics are formed
The modern method of classification which is based on comparisons of base sequences of genes or aa sequences of proteins. DNA mutations accumulate gradually and at a roughly constant rate. So they can be used as a molecular/ evolutionary clock. Species that have a recent common ancestor have few differences in sequence and are more closely related- species that diverged far back in evolution have many differences in sequence and are less closely related.
What are cladograms?
Tree diagrams that show the most probable sequence of divergence in clades. They also dhow how recently two groups diverged from their common ancestor
What is a clade?
A group of organisms that evolved from a common ancestor
What are nodes?
The branching points on cladograms. They represent the common ancestor
What do the length of lines indicate in a cladogram?
The time since the split
What are examples of reclassification?
Reclassification of primates
Reclassification of the figwort family
Reclassification of all organisms in three domains
Describe the reclassification of primates
Humans belong to the order Primates and the family Hominidae
Based on traditional classification all great apes were placed to a different family than humans
Using the number of differences in base sequences of mitochondrial DNA as an evolutionary clock, primates were reclassified. Chimpanzee and bonobo are most closely related to humans.
Describe the reclassification of the figwort family
The figwort family of plants used to contain 275 genera. Cladograms showed that species in the family were not a true clade as not all species share a recent common ancestor. Therefore, the family was massively reclassified and less than half of the species have been retained in the family.
- Some genera were moved to existing families
- Some genera were moved to newly created families
- Two small existing families were merged with the figwort family
Describe the reclassification of all organisms in three domains
Living organisms used to be classified into five kingdoms: one with prokaryotes and four with eukaryotes. The kingdom was the highest taxon. When base sequences were compared, two different groups of prokaryotes were identified which are different from each other as from eukaryotes. Thus a higher taxon was created to reflect this: the domain
All organisms are classified as: Archaea, eubacteria, Eukaryota
- The original evidence came from comparisons of DNA coding for ribosomal RNA
Describe the features of eubacteria
Nucleus and membrane bound organelles: absent
Chromosomes: circular
Proteins associated with DNA: absent
Introns: absent or rare
Cell wall: made with peptidoglycan
Cell membrane: glycerol-esters lipids
Environment they live in: not in extreme environments
Describe the features of archaea
Nucleus and membrane bound organelles: absent
Chromosomes: circular
Proteins associated with DNA: present
Introns: present in some genes
Cell wall: not made of peptidoglycan
Cell membrane: glycerol-ether lipids
Environment they live in: found in extreme environments
Describe the features of eukaryota
Nucleus and membrane bound organelles: present
Chromosomes: linear
Proteins associated with DNA: present
Introns: frequent
Cell wall: not made of peptidoglycan/ not always present
Cell membrane: glycerol-esters lipids
Environment they live in: not in extreme environments
List the main plant phyla
Bryophyta
Filicinophyta
Coniferophyta
Angiospermophyta
Describe the features of Bryophyta
Vegetative organs: No roots, no stems, no leaves
Vascular tissue: no
Reproductive structures: No pollen/ovules/flowers/seeds/ fruits - spores produced in a capsule
Describe the features of Filicinophyta
Vegetative organs: Roots, leaves( often divided into pairs of leaflets), stems
Vascular tissue: Both present
Reproductive structures: No pollen/ovules etc. Spores are produced in sporangia
Describe the features of Coniferophyta
Vegetative organs: Roots, leaves (narrow), stems
Vascular tissue: Both present
Reproductive structures: no flowers/fruits, pollen produced in cones, ovules produced in female cones, seeds are produced and dispersed
Describe the features of Angiospermophyta
Vegetative organs: Roots, leaves, woody stems
Vascular tissue: Both present
Reproductive structures: Pollen produced, ovules produced, seeds produced and fruits develop
Describe the features of porifera
Body openings: no mouth or anus
Symmetry: none
Skeleton: internal spicules
Body segmentation: unsegmented
Other features: pores in the body, attached to a surface, varied shapes
Describe the features of cnidaria
Body openings: Mouth only
Symmetry: Radial
Skeleton: Soft; but hard corals secrete CaCO3
Body segmentation: unsegmented
Other features: Tentacles around the mouth
Describe the features of platyelminthes
Body openings: Mouth only
Symmetry: bilateral
Skeleton: soft, no skeleton
Body segmentation: Unsegmented
Other features: Flat thin bodies, no blood no gas exchange
Describe the features of mollusca
Body openings: Mouth and anus
Symmetry: bilateral
Skeleton: most have shall made of CaCO3
Body segmentation: unsegmented
Other features: body composed of mantle, muscular foot and visceral mass
Describe the featured of annelida
Body openings: Mouth and anus
Symmetry: bilateral
Skeleton: Internal cavity with fluid with pressure
Body segmentation: Segmented
Other features: Bodies with many rings shaped segments, bristles often present
Describe the features of arthropoda
Body openings: Mouth and anus
Symmetry: bilateral
Skeleton: Exoskeleton made of chitin
Body segmentation: Segmented
Other features: Jointed legs
Describe the features of chordata
Body openings: Mouth and anus
Symmetry: bilateral
Skeleton: internal skeleton
Body segmentation: segmented
Other features: At least at embryonic state- may persist in adulthood: notochord, dorsal nerve cord, pharyngeal gill slits, post-anal tail
Describe the features of a bony-ray finned fish
Skin: Skin with scales
Gas exchange: gills
Limbs: no limbs, fins
Reproduction: external fertilisation, eggs
Body temperature: not constant body temp (poikilothermic)
Describe the features of amphibians
Skin: soft, moist, permeable skin
Gas exchange: breathe through skin and simple lings with small internal folds
Limbs: four legs when adults, pentadactyl limbs
Reproduction: External fertilisation, eggs coated with protective jelly
Body temperature: not constant body temp (poikilothermic)
Describe the features of reptiles
Skin: Dry, impermeable skin with scales
Gas exchange: lungs with extensive folding
Limbs: four legs, pentadactyl limbs
Reproduction: Internal fertilisation, lay eggs with soft shells
Body temperature: not constant body temp (poikilothermic)
Describe the features of birds
Skin: Skin with feathers
Gas exchange: Lungs
Limbs: Two wings and two wings, pentadactyl limbs
Reproduction: Internal fertilisation, lay eggs with hard shells
Body temperature: constant body temp (homeothermic)
