Notes : 5.17 + 5.19 - Natural selection, Evolution and speciation Flashcards
Define the term evolution
The frequency of an allele in a population changes over time due to natural selction
Explain the process of evolution by natural selection
- M : Random mutation causes alternative version of a gene whihc leads to differnt allels.
- V : This creates genetic variation between individuals of the same species (intraspecific variation)
- A : A selection pressure occurs which means that organisms on the most adapted to their environment survive and reproduce. ( Bacteria don’t reproduce the multiply or instead say that they reproduce asexually in an exam)
- A : Passing on the advantageous allele.
- T : Over time the frequency of the beneficial allele increases from generation to generation
Name all the evidence you know for evolution
- Genomics (required to know)
- Proteomics (required to know)
- DNA hybridisation
- DNA profiling/fingerprinting
- Protein sequencing
- Fossils
How does genomics provide evidence for evolution ?
- DNA technology is used to determine the base sequence of an organism genome.
- This allows scientist to make comparisons between organisms DNA.
- If the bases sequences are similar of two species they are closely related and share a common ancestor,
- If the base sequences are less similar for two species they are not closely related.
What is proteomics
The study of proteins
How does proteomics provide evidence for evolution
- The sequence of amino acids in a protein is coded for by the DNA sequence in a gene
- Related organisms have a similar DNA sequences and so similar amino sequences in their protein
- The amino acid sequences of some proteins are very similar across many different species;this indicates common ancestry.
The level of similarity between amino acid sequences of equivalent proteins can give a
measure how long ago two species diverged from each other Knowing how long ago a species diverged from a common ancestor enables scientists to establish the relationships between organisms
How does DNA hybridisation provide evidence for evolution
- If we mix a 2 single strand of DNA from two different species together their DNA stands will nybrisies together forming hydrogen bonds with complementary bases creating a double helix
- Species that are similar will form more hydrogen bonds as they have similar base sequencing.
- A Lot of energy will be required to break these bonds
- We know that if the temperature required to break these bonds are higher then the species are closely related as there bases sequeung is similar causing them to have more hydrogen bonds.
- Conversely, if it separates easily at lower temperatures, it suggests that the species are more distantly related.
How does fossils provide evidence for evolution ?
Fossils provide a record of how creatures evolved and how this process can be represented by a ‘tree of life’, showing that all species are related to each other.
The role of the scientific community in validating new evidence
- Scientific journals
- Peer review process
- Scientific conferences
Blurt everything you know about Scientific journals
- Scientist publish their new discoveries
Blurt everything you know about Peer Review
- Scientist check that studies are carried out in
such a way that results will be valid, and that results have been analysed
appropriately e.g.by the use of the correct statistical tests. - Check that it supports conclusions
Blurt everything you know about conferences
- A scientific conference is a gathering of scientists in a particular field of study from all over the world
- Scientists can present their findings for questions and discussion
Conference Members have the opportunity to speak with each other about their work and to share ideas and concerns
What is speciation
The development of a new species
How does speciation occur ?
- When populations of the same species become reproductively isolated, reducing gene flows (transfers between genes) between two populations.
What causes variation
- Mutations
- Independent assortment
- Crossing over
Define the term allele frequency
The relative frequency of a particular allele in a population
Define the term gene pool
All of the genetic information, including all variations, contained within a population of a particular species at a particular time
How does reproductive isolation
Due to :
- Geographical isolation (allopatric speciation)
- Random mutations produce changes in a phenotype that prevents populations from mating (sympatric speciation)
Blurt everything you know about allopatric speciation
- It occurs when populations are geographically isolated. (e.g due to physical barriers) - Thebarriercouldbenatural e.g.a bodyofwateror a mountain range
It Can also be man-made.g.a motorway - This prevent groups from mating. Causing reproductive isolation. So there is no gene flow between them
- Natural selection occurs(explain this process in an exam) as if they are geographically isolated they will experience different conditions so will experience different selection pressures acting on them so there will be changes in the allele frequency.
What is sympatric speciation and how can it occur ?
- Its when species become reproductively isolated even though there is no geographical isolation.
- This can happen through a number of ways :
- Seasonal changes
- Mechanical changes
- Behavioural changes
Explain how seasonal changes lead to reproductive isolation reducing gene flow causing sympatric speciation
Seasonal changes can cause individuals from the same population to develop different flowering or mating seasons, or become sexually active at different times of the year.
- This will reduce the interberreding causing them to become reproductively isolated and so sympatric speciation occurs
Explain how mechanical changes reduces gene flow, leading to reproductive isolation causing sympatric speciation
- This refers to physical alteration in the organism
- changes in genitalia prevent successful mating. Which reduces gene flow, leading to reproductive isolation causing sympatric speciation
Explain how behavioral changes reduces gene flow, leading to reproductive isolation causing sympatric speciation
- When a group of individuals develop courtship rituals that aren’t
attractive to the opposite sex they won’t mate with the opposite sex. This reduces the gene flow between them and the main population, leading to reproductive isolation causing sympatric speciation
The fruit fly example of sympatric speciation
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