Flashcards in Evolution 2 Deck (52):
What is microevolution?
The change in frequency in alleles in a population over time.
What are the four processes that effect microevolution?
What is a gene?
A sequence of nucleic acid coding for a function.
What is an allele?
Different variants of a particular gene.
What is mutation?
Mutation is the ultimate source of novelty and can be advantageous or often more harmful (deleterious). The rate of mutation is low and isn't fast enough to drive evolution by itself.
Describe selection through mutation.
Mutation creates variation.
Unfavourable mutations are selected against.
Reproduction and mutation occur.
Favourable mutations more likely to survive and reproduce.
What is genetic drift?
This is when there are changes in allele frequencies by chance.
Where is genetic drift most important?
In small populations.
What is gene flow?
Exchange of alleles between populations.
What is the classical theory of evolution?
Selection removes genetic variation by favouring alleles that confer greater fitness.
What is the balance theory of evolution?
Selection maintains genetic variation by favouring heterozygotes, or by favouring different alleles in different times and places.
What is the neutral theory of evolution?
Most genetic variation maintained by genetic drift of alleles conferring no selective advantage.
What is the shifting balance theory for evolution?
In populations that are subdivided, both random genetic drift and gene flow can become very important in evolution.
What is sickle cell anaemia?
A hereditary disease that affects haemoglobin.
What causes sickle cell anaemia?
A mutation in the DNA code for the beta chain of haemoglobin causes glutamic acid to be replaced by valine at position 6.
What is sickle cell anaemia an example of?
What is the relationship between malaria and sickle cell anaemia?
Areas where there is malaria, there is a high amount of sickle cell anaemia through natural selection as those with sickle cell anaemia can't get malaria due to the shape of the blood cell.
What will homozygotes get?
(HH) Malaria or (SS) sickle cell anaemia.
What will heterozygotes get?
(HS) Which will show minor symptoms of sickle cell anaemia but won't enable the person to get malaria.
What happens to the sickle cell anaemia allele when malaria is absent?
Natural selection acts to eliminate the sickle cell allele (S)
What is a species?
Smallest independently evolving unit
When is evolution independent?
When mutation, selection and gene flow operate independently.
What is the Morphological species concept?
Species defined as organisms with shared morphological features.
Many species with shared morphology can't interbreed e.g - Mimics.
Many species that vary morphologically can interbreed e.g - Domestic dogs.
Shows incompleteness of speciation.
What is the biological species concept?
Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.
What are the practical problems with the biological species concept?
Fossil species (Lack information)
Incompleteness of speciation.
Why is there variation across a geographical range?
Because individuals tend to mate with others nearby and those at the extremes of a distribution do not normally meet.
In apparent uniform habitats, individuals exist within separate populations which can lead to the formation of new species due to natural selection.
What is a cline?
When individuals vary continuously across their range.
What is the Phylogenetic species concept?
A species is the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent.
What are the advantages of the phylogenetic species concept?
It is applicable to asexual and extinct groups.
What are the disadvantages of the phylogenetic species concept?
This definition greatly increases the number of named species.
Defining a 'diagnosable cluster' has same problem as defining morphological species.
What is the evolutionary species concept?
A species is a single lineage of ancestor-descendant populations which maintain its identity from other such lineages and which has its own evolutionary tendencies and historical fate.
What are the advantages of the evolutionary species concept?
Applicable to asexual and distinct groups.
Not so dependant on arbitrary morphological groupings.
What are the dis advantages of the evolutionary species concept?
Why is reproductive isolation a key to speciation?
Reproductive isolation between two populations prevents gene flow between them which allows for selection and drift to change gene frequencies independently - leads to distinct phenotypes.
What are the features of prezygotic isolation?
Incompatibility of mating structures.
Sperm unable to fertilize egg.
What are features of prezygotic isolation?
Hybrid has low survival.
Give an example of prezygotic isolation.
1000 species of Drosophila on Hawaii have evolved from a single ancestral species.
Give an example of behavioural isolation?
Long and complex mating rituals prevent the species from interbreeding.
Give an example of mechanical isolation.
The pedipalps of male spiders have a complex structure that only fits the reproductive openings of the same species of female.
Give an example of gamete compatibility.
Plant and animal fertilization.
What is ecological isolation and give an example?
Occupy different niches.
What is temporal isolation?
Reproductively active at different times.
What is geographical isolation and give an example.
Reproductively active in different places.
E.g - Different pollinators select different flower morphs and symbiont specialization drives some speciation.
What are the problems with postzygotic isolation?
How does allopatric speciation come about?
Genetic drift, selection and mutation.
What is pleiotropy?
Gene/group of genes have more than one effect.
What is 'hitchhiking'?
Selected genes closely linked to genes involved in reproduction.
How does post zygotic isolation evolve?
All genotypes containing mutant 'a' and mutant 'b' have lower fitness.
Different mutant appears in each population.
What is epistasis?
Effect of gene depends on other genes in the genome.
What is the hypothesis for allopatric speciation?
When allopatric speciation is incomplete when diverging populations come together, natural selection will promote the evolution of isolating mechanisms.
What is sympatric speciation?
When a species occupies an area with more than one niche, subpopulations specialising on those niches may occur.