Natural Selection Flashcards
What are Darwin’s observations and deductions
- Species are reproduce: species are aware of springs produced are not all going to survive so by producing then someone still survive because of survival of the fittest.
- Population tend to remain fairly constant: since there is a struggle for survival individuals are eaten or die diseases so the population dies out.
- That is variation within a species: those with beneficial adaptations or characteristics that help them in their environment are more likely to survive and reproduce.
- Offsprings often resemble their parents - characteristics are inherited: those who survive and reproduce have the most beneficial characteristics to pass to the next generation.
What are Darwin’s deductions?
1) There is a struggle for survival. Individuals get eaten, die of disease or competition for resources.
2) individuals with characteristics that best adapt for their environment are more likely to survive and reproduce.
3) If these characteristics can be inherited, then the organism will pass them onto their offspring.
What is evidence for evolution?
1) fossil different species were alive in the past these have become extinct a new species have arisen.
2) fossil remains show species getting more and more complex as time goes on while retaining similarities. It also shows extinction and arrival of forms this evidence can be used to build phylogenetic trees.
What are problems with fossil records?
- there is suspected fake fossils
- fossils records tend to be incomplete
- usually only the hard parts of the animal fossil remain and many organisms do not have hard parts
- They are only formed in certain conditions
- can be destroyed by movement of rocks .
What is the most recent evidence for evolution?
- biological molecules: many biological molecules are found in all organisms suggesting that all species are raised from one common ancestor. Closely related to species have more similarities.
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protein variation: vital proteins such as DNA/RNA primaries are found in all living organisms. Higher organisms have added sub units that improve regulation.
-cytochrome c protein used in respiration shows pattern of changes. More change = more evolutionary distance. -
dna: sequencing the bases in DNA allows for comparison more differences found means that there is greater evolutionary distance
-mitochondria are passed offspring in the egg during sexual reproduction. mutations in the mitochondria are more common as mitochondrial DNA as less to checking occurs compared to genomic nuclear DNA
Variation can be used to trace human evolution
What is adaption?
Adaption is a feature that enhances survival and long-term reproductive success
What should a well adapted organism be able to do?
- find enough feed/photosynthesise at a fast enough rate
– find enough water plus mineral ions
– Defend itself from predators and diseases
– Survive the physical condition of its environment such as temperature, water availability and light intensity
– Respond to changes in its environment
– Be able to reproduce successfully
What is behaviour adaptation?
- This is when an aspect of a behaviour of the organism that allows it to survive where it lives
– Innate : inherited from genes
– Learned behaviour: learned from experience or observing other animals
What are examples of behavioural adaptations?
– Survival behaviours: animals play dead or a rabbit freezes in danger
– **Court ship: exhibit elaborate courtship behaviours to attract a male scorpions perform a dance
– Seasonal behaviours : help organisms in environment
Migration: move from one region to another them back if conditions are better
Hibernation : a period of inactivity
– Caterpillars are able to act like ant through sound and imitation so answer rescue it and take it back to the nurse and the caterpillar eats the baby ants
What is physiological adaptations?
- An internal and biochemical feature that assure the correct functioning of cell processes
What are examples of physiological adaptations??
– poison production: produce venom and plants produce poison
– Antibiotic production : bacteria produce antibiotic
– water holding: stool water in the body for long periods of time
– Mutations occur organisms are able to detect chemicals and poison
– Higher affinity for oxygen
What are Anatomical adaptation?
– Any structure that enhances the survival of the organisms
What are examples of anatomical adaptations?
– Teeth: shape and type of teeth are To its diet
– Camouflage : the colour of an animal blend into its environment making it hard to sport
– Body covering : hairs scales spines
– himiary : copy animals appearances or songs to allow a harvest pray to protect themselves from predators
- barnacles in a place where there isn’t much food have either wide opening to the shells shell and thick shells
What is convergent evolution?
Adaptations are controlled by the environment. This means that evolutionary distant species that live in similar habitats or exploit similar ecological niche of them evolve similar adaptations.
What is natural selection?
Genetic variation
Random mutations cause different alleles of genes
This causes intraspecific variation within a species.
Very occasionally new alleles may be beneficial
Selection pressure
Organisms have to compete for survival
Selection pressure are environmental factors that greater chances of survival for others, hence will production for some members of a proper and lower chances for others.
Selection pressure includes availability of suitable food, predators , diseases, physical or chemical factors and different habitats have different selection pressures .
Reproductive success
Organisms with advantageous adaptations are more likely to survive and reproduce.
They pass on all that code for beneficial characteristics to their offsprings
** repeated over many generations**
This process is repeated over many generations so the beneficial allele becomes more frequent in the population population therefore the proportion of the population possessing the advantages characteristic increases 
What are implications of evolution for human populations?
- The use of pesticides by humans creates a selection pressure for those individuals with some form of resistance to the insecticide.
Resistance develops in different ways: - Insects may be able to metabolise the insecticide
- Target receptor proteins on the cell membrane may be modified
What does pesticide resistance lead to?
Many insect species carry diseases therefore infection rates climb.
- Pesticides become concentrated in the food chain. Large numbers survive the insecticide application, but hold it in their bodies. Predators eat these insects and get a large dose of insecticide. Bioaccumulation can occur.
- Insects can cause a great deal of damage before insecticide resistance is recognised by farmers. Crop loss can occur.
- Broader (and stronger) insecticides may need to be used, killing beneficial or benign insects.
- Resistance requires the development of new pesticides – a costly exercise.
What is stabilising selection?
- If the environment is stable then stabilising selection occurs: the same alleles are ‘selected for’ in every successive generation and the gene pool of the population remains roughly the same.
- Extremes of phenotype are selected against.
- Intermediate phenotypes are selected.
- an example is barn owls which can’t be too big or too small
What is directional selection?
- If the environment changes there will be a change in the selection pressure on the population.
- Directional selection is an evolutionary force of natural selection.
- One extreme will be selected against and the other will have a selective advantage.
- Over time the allele frequency shifts towards an extreme.
- An example is Harley Quinn beetles have long legs protect lady Beatles so long legs is passed onto the offspring
Describe genetic drift
- Random fluctuations can occur in allele frequency within a population – purely by chance.
- Most likely in small populations – e.g. on islands where populations are geographically separated.
- It occurs simply because of the randomness of reproduction.
- In extreme cases an allele may be eradicated from a population entirely.
What is genetic bottleneck?
- A natural disaster or disease pandemic may kill a large percentage of a population.
- This may by chance lead to particular alleles being lost from the population.
- Genetic diversity is reduced.
What is the founder effect?
- When a new population is started from only a few individuals it may show a loss of genetic variation.
e.g. The Amish population in North America all descend from a small number of people and suffer from several genetic disorders
Assessing genetic diversity
- Alleles are different forms of a gene found at the same locus (position on a chromosome)
- Greater variety in the alleles in a population allows for better adaptation to a changing environment
- Low genetic diversity can lead to problems associated with inbreeding (recessive conditions)
- Mutations and interbreeding between populations increase genetic biodiversity
- Selective breeding, captive breeding, cloning, genetic bottlenecks, the founder effect and genetic drift can reduce genetic diversity
- Most genes are monomorphic – all members of the population have the same allele (basic structure and biochemistry is constant within a species)
- Some genes are polymorphic – there are two or more alleles of a gene (genetic variation)
- The proportion of polymorphic gene loci indicates the genetic biodiversity in the population
█(𝑷𝒓𝒐𝒑𝒐𝒓𝒕𝒊𝒐𝒏 𝒐𝒇 𝒑𝒐𝒍𝒚𝒎𝒐𝒓𝒑𝒉𝒊𝒄 𝒈𝒆𝒏𝒆 𝒍𝒐𝒄𝒊=” “ @@𝒏𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒑𝒐𝒍𝒚𝒎𝒐𝒓𝒑𝒉𝒊𝒄 𝒈𝒆𝒏𝒆 𝒍𝒐𝒄𝒊)/(𝒕𝒐𝒕𝒂𝒍 𝒏𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒍𝒐𝒄𝒊)
What is speciation?
- Large populations can be split into sub-groups by an isolating mechanism; geographical or reproductive barrier.
- The selection pressures may be different in each population or genetic drift may occur, changing the gene pool of each population, until eventually the two sub-groups may not be able to breed together, at which point they are classified as separate species.
What is geographical isolation also known as allopatric speciation?
Geographical Isolation
- Physical barriers (eg mountain range, river, ocean) can separate a population into two breeding groups.
- Different selection pressures will act on the two populations.
Selection, genetic drift and mutations will lead to different gene frequencies in the two populations.
- This is allopatric speciation
What is reproductive isolation known as Sympatric isolation?
- Two groups of organisms may be isolated from breeding together even if they live in the same place.
- There are various reasons why groups of organisms may breed:
-Different courtship behaviour - Mechanical problems – eg different sizes!
- Gamete incompatibility
- Zygote inviability
- Hybrid sterility
This is
sympatric speciation
What are ecological barriers?
- Two groups may live in the same area but rarely meet. e.g. Insects living in different species of tree in a wood. Crayfish living in streams or ponds.
What are temporal /seasonal barriers?
- Two groups may live in the same habitat but may not be active at the same time of year or day.
Eg two species of flowering shrub both live in the same area of Western Australia but one flowers in summer and the other in winter.
What is artificial selection?
- Humans select the alleles for the best characteristics.
- Breeders will select individuals with desired characteristics to breed and prevent other individuals breeding. This is repeated over many generations.
What is artificial selection in dairy cow?
- Breeders select cows with high milk yields to reproduce.
- Bulls which have progeny with high milk yields are used.
- The process is repeated over many generations.
- Artificial Insemination is commonly used to maximise the number of cows a bull can fertilise.
- Embryo transplantation is sometimes used to increase the number of offspring that one cow can have.
- Embryo cloning – to produce more identical embryos
What is artificial selection in bread wheat?
- Wheat has been bred for various characteristics – high yield, resistance to infections, high protein content, resistance to wind and rain damage.
- The resulting wheat is a hybrid of all these species and hence has 42 chromosomes in each cell. 6n = polyploid
- The three species have been bred together in the past over time to produce the modern variety.
What are the problems with artificial selection?
- Artificial selection reduces genetic diversity.
- Inbreeding often occurs increasing the chances of two recessive alleles of a gene coming together – inbreeding depression.
- Characteristics selected for may cause health problems for the organism.
- If the environment changes we may not have the gene pool to breed crops or livestock that can survive them.
What are solutions for artificial selection?
- Breeders may decide to cross two different varieties to increase hybrid vigour.
- Gene banks may be created including ‘wild types’ e.g. rare breed farms, seed banks, frozen embryos sperm, eggs.
What are the differences between natural selection and artificial selection?
Natural selection
- Environment = selection agent
-Slow
- benefits species
- survival of the fittest
- whole genotype selected
- changes in gene frequencies
Artificial selection
- Humans = selection agent
- Fast
- benefits humans
May be detrimental to the organism
- few traits selected
- changes in gene frequencies
