Speciation
Biological Evolution - the genetic change in a population from one generation to another
Speciation - The formation of a new species, the result of reproductive isolation
Gene Pool - The number of alleles that occurs in a population
Populations are the units of evolution and changes in allele frequency in the gene pool of a population indicates that evolution is occurring.
Deme - A local population that has no or limited gene flow with members of other populations.
Cline - A gradient of variation
Clinal Variation - Must be linked in some way to an environmental gradient. There are two possible mechanisms:
Due to environmental differences - in this case the cline would be purely phenotypic
Due to genetic differences resulting from selection
Ring Species - A special case of cline in which the two ends of the cline join to form a loop or ring. (When it is hard to achieve geographic isolation)
When individuals migrate between populations and interbreed. Introduces their alleles into populations.
Gene Flow - The movement of alleles carried by individuals between populations.
Immigration - Individuals move into a population
Emigration - Individuals move out of a population
Gene flow can:
Increase genetic differences between populations by introducing new alleles. Significant if a barrier isolates populations once migration has happened so that no further gene flow can occur
Decrease genetic differences between populations - If migration is regular and involves large numbers of individuals, accumulated genetic differences between populations can be reduced by gene flow
Genetic Drift - A change in allele frequency due to the accumulated effects of chance
Genetic drift occurs in small populations and with alleles not greatly affected by selection.
Founder Effect - When a small number of individual animals or plants are dispersed to a distant place, the new arrivals carry only a small portion of the gene pool of the ‘parent’ population. The alleles of the colonists are therefore only a sample (not representative) of the parent gene pool. It is a largely a matter of chance which alleles are present in the pool.
Occurs when a large population is suddenly reduced in size, due to either a catastrophic environmental event or human impact. Bottleneck may randomly alter allele frequencies and/or remove alleles so that when the population recovers, allele frequencies may not be representative of the original population and genetic diversity is likely to be reduced.
Commonly used in selective breeding. It increases the chances of favourable alleles coming together and resulting in desirable phenotypes.
Inbreeding has a large affect on small populations such as a founder population.
Increases the proportion of homozygotes in the population similar to self-fertilisations
results in rare recessive alleles being expressed.
results in less diverse genetics in a population.
Increases the number of heterozygotes in a population and reduces the chances of unfavourable and harmful recessive alleles coming together.
Offspring produced by outbreeding show hybrid vigour when they contain a variety of alleles from their genetically different parents. These organisms tend to have greater evolutionary fitness compared to inbred offspring.
Where inheritable traits that make an individual more likely to survive long enough in its environment to reproduce become more common in the population over successive generations.
Abiotic and Biotic environmental factors influence which individuals survive (they exert selection pressures on the population).
Extreme phenotypes are selected against and average phenotypes are selected for
Individuals at both extremes of the distribution are selected for simultaneously. Average phenotypes are at a disadvantage and are selected against
A single phenotype is selected for and the allele frequency shifts in one direction.
Males (or females) compete for partners with the heritable characteristics of the ‘winners’ being passed on.
Evolutionary trees drawn as a branching diagram. Shows the inferred evolutionary relationships between taxa.
Inferred relationships are based on:
Similarities and differences in their molecular biology (DNA)
Similarities and differences in their physical characteristics.
Where taxa join at their bases in a phylogenetic tree (nodes) indicates the existence of a common ancestor that the groups have descended from. Each line of the tree represents time.
Phylogenetic tres shows Divergent Evolution.
Refers to the number of chromosomes in a cell. Uncommon in animals. Numerical changes in chromosomes have been important in the evolution of over a third of all flowering plant species.
Genome - The entire component of genetic material in an organism
Haploid - The number of chromosomes in the gamete
Diploid - The number of chromosomes in the zygote
Monoploid - The number of chromosomes in each set (Haploid and Monoploid are interchangeable)
Aneuploidy - Only certain chromosomes are represented an unusual number of times
Euploidy - Variation in chromosome number involves the entire genome.
Involves the multiplication of the entire genome within a single species.
Autotriploid has 3 sets of chromosomes. Autotetraploid has 4 sets.
Results from the failure of chromosomes to separate during the first or second division of meiosis or in mitosis (results in a tetraploid) because the spindle does not function properly. All the chromosomes finish up in the same nucleus, which has twice as many chromosomes as it should have.
Reduces infertility
More important in evolution than autopolyploids.
Results from hybridisation between species.
Rare in Animal Kingdom.
Occurs in animals that reproduce parthenogenetically (without fertilisation)
Divergent - Occurs when species become different. It leads to Diversity in Species. Does share common ancestor.
Convergent - Occurs when species become similar. It leads to lack of genetic diversity. Doesn’t share common ancestor. Similar due to selection pressures. Results in analogous structures.
Parallel Evolution - when two or more related species evolve along similar lines independently.
Co-Evolution - occurs when two species form a mutalistic relationship. It leads to Extinction as if one species dies, the other will also die. Doesn’t share common ancestor. A change in feature of one species acts as a pressure for the change in another species.
Vicariance - Large-scale allopatric speciation of a taxonomic group by a significant geophysical event
a type of divergent evolution. Involved rapid evolution of a large number of species from an ancestral group to occupy a variety of different ecological niches that may have become available suddenly.
Can arise in two different ways
evolution of a new structure, physiology or behaviour enabling exploitations of a different aspect of habitat
geographical isolation from competitors or predators
One form to another.
The transitional forms in the fossil record in response to natural selection
Involves the formation of many different species that are no longer closely related.
features similar in structure and origin but different in function. Similiarity in structure indicates common ancestry, while difference in function indicates adaption to different selection pressures in different environments. Can be seen in the limbs.
Structures with different evolutionary orignings that appear very similar because they carry out the same or similar functions.
The formation of new species resulting from populations becoming reproductively isolated; gene flow no longer occurs.
Speciation can occur:
gradually by the slow accumulation of small changes
instantly by the changes in chromosome number through polyploidy
Sympatric Species - are (closely) related species that live in the same geographic location.
Allopatric Species - are (closely) related species that live in different geographic location.
Reproductive Isolating Mechanism (RIM) - any factor that stops members of populations of the same spceices or members of different species from breeding together; it acts as a barrier to gene flow.
RIMS can be;
Prezygotic - act before the egg is fertilised
Postzygotic - act after the egg is fertlilised
Reproductive isolation may result from just one or a combination of prezygotic and/or postzygotic isolating mechanisms.
Geographical isolation results from physical barriers (rivers, mountains, oceans) separating populations. If the population come together again later, they are sufficiently different (as a result of selection pressures) that they do not/ unable to breed.
Results from the fact that the differences in structure of the external reproductive organs do not allow for the transfer of sperm between sexes.
Resutls from differences in habitat within the same geographical area, so that the populations rarely come in contact with each other.
Results from breeding behaviour occurring at different non-overlapping times. This can be saily or seasonal differences in timing of mating.
Results from differences in behaviour, typically mating behaviour such as courtship
Can also result from different activity patterns.
Results from the incompatibility of gametes. Sperm may not be able to fertlise an egg of another species because:
The egg’s surface does not have the correct chemical receptors
Sperm cannot penetrate the surface of the egg
Sperm cannot survive in the chemical environment of the female reproductive system
the zygote, embyo or offspring is inevitable so it dies early in its development
The hybrid reaches maturity but is infertile so it cannot breed
Occurs when the hybrid reaches maturity and is able to breed but the next generations are infertile or have reduced reproductive capability
Allopatric speciation is the process where speciation cannot occur until a population has divided into two or more geographically isolated populations.
Most common form of sympatric speciation is instant speciation. This involves the formation of polyploid therefore is more common in plants.
Less important that allopatric speciation
If populations become sympatric three things can happen:
Interbreeding
Populations do not hybridise
They hybridise freely and merges to form the original single species.
Through polyploid. Results in the evolution of many plant species. Results in a new species in a single generation due to the consequent formation of the postzygotic reproductive barrier of hybrid sterility.
Allopolyploidy is the more important of the two as it results in the hybrids containing the genes of two different species which can be advantageous to the polyploid should the selection pressures change.
Mountain building and changes in sea level
Biological Evolution - the genetic change in a population from one generation to another
Speciation - The formation of a new species, the result of reproductive isolation
Gene Pool - The number of alleles that occurs in a population
Populations are the units of evolution and changes in allele frequency in the gene pool of a population indicates that evolution is occurring.
Deme - A local population that has no or limited gene flow with members of other populations.
Cline - A gradient of variation
Clinal Variation - Must be linked in some way to an environmental gradient. There are two possible mechanisms:
Due to environmental differences - in this case the cline would be purely phenotypic
Due to genetic differences resulting from selection
Ring Species - A special case of cline in which the two ends of the cline join to form a loop or ring. (When it is hard to achieve geographic isolation)
When individuals migrate between populations and interbreed. Introduces their alleles into populations.
Gene Flow - The movement of alleles carried by individuals between populations.
Immigration - Individuals move into a population
Emigration - Individuals move out of a population
Gene flow can:
Increase genetic differences between populations by introducing new alleles. Significant if a barrier isolates populations once migration has happened so that no further gene flow can occur
Decrease genetic differences between populations - If migration is regular and involves large numbers of individuals, accumulated genetic differences between populations can be reduced by gene flow
Genetic Drift - A change in allele frequency due to the accumulated effects of chance
Genetic drift occurs in small populations and with alleles not greatly affected by selection.
Founder Effect - When a small number of individual animals or plants are dispersed to a distant place, the new arrivals carry only a small portion of the gene pool of the ‘parent’ population. The alleles of the colonists are therefore only a sample (not representative) of the parent gene pool. It is a largely a matter of chance which alleles are present in the pool.
Occurs when a large population is suddenly reduced in size, due to either a catastrophic environmental event or human impact. Bottleneck may randomly alter allele frequencies and/or remove alleles so that when the population recovers, allele frequencies may not be representative of the original population and genetic diversity is likely to be reduced.
Commonly used in selective breeding. It increases the chances of favourable alleles coming together and resulting in desirable phenotypes.
Inbreeding has a large affect on small populations such as a founder population.
Increases the proportion of homozygotes in the population similar to self-fertilisations
results in rare recessive alleles being expressed.
results in less diverse genetics in a population.
Increases the number of heterozygotes in a population and reduces the chances of unfavourable and harmful recessive alleles coming together.
Offspring produced by outbreeding show hybrid vigour when they contain a variety of alleles from their genetically different parents. These organisms tend to have greater evolutionary fitness compared to inbred offspring.
Where inheritable traits that make an individual more likely to survive long enough in its environment to reproduce become more common in the population over successive generations.
Abiotic and Biotic environmental factors influence which individuals survive (they exert selection pressures on the population).
Extreme phenotypes are selected against and average phenotypes are selected for
Individuals at both extremes of the distribution are selected for simultaneously. Average phenotypes are at a disadvantage and are selected against
A single phenotype is selected for and the allele frequency shifts in one direction.
Males (or females) compete for partners with the heritable characteristics of the ‘winners’ being passed on.
Evolutionary trees drawn as a branching diagram. Shows the inferred evolutionary relationships between taxa.
Inferred relationships are based on:
Similarities and differences in their molecular biology (DNA)
Similarities and differences in their physical characteristics.
Where taxa join at their bases in a phylogenetic tree (nodes) indicates the existence of a common ancestor that the groups have descended from. Each line of the tree represents time.
Phylogenetic tres shows Divergent Evolution.
Refers to the number of chromosomes in a cell. Uncommon in animals. Numerical changes in chromosomes have been important in the evolution of over a third of all flowering plant species.
Genome - The entire component of genetic material in an organism
Haploid - The number of chromosomes in the gamete
Diploid - The number of chromosomes in the zygote
Monoploid - The number of chromosomes in each set (Haploid and Monoploid are interchangeable)
Aneuploidy - Only certain chromosomes are represented an unusual number of times
Euploidy - Variation in chromosome number involves the entire genome.
Involves the multiplication of the entire genome within a single species.
Autotriploid has 3 sets of chromosomes. Autotetraploid has 4 sets.
Results from the failure of chromosomes to separate during the first or second division of meiosis or in mitosis (results in a tetraploid) because the spindle does not function properly. All the chromosomes finish up in the same nucleus, which has twice as many chromosomes as it should have.
Reduces infertility
More important in evolution than autopolyploids.
Results from hybridisation between species.
Rare in Animal Kingdom.
Occurs in animals that reproduce parthenogenetically (without fertilisation)
Divergent - Occurs when species become different. It leads to Diversity in Species. Does share common ancestor.
Convergent - Occurs when species become similar. It leads to lack of genetic diversity. Doesn’t share common ancestor. Similar due to selection pressures. Results in analogous structures.
Parallel Evolution - when two or more related species evolve along similar lines independently.
Co-Evolution - occurs when two species form a mutalistic relationship. It leads to Extinction as if one species dies, the other will also die. Doesn’t share common ancestor. A change in feature of one species acts as a pressure for the change in another species.
Vicariance - Large-scale allopatric speciation of a taxonomic group by a significant geophysical event
a type of divergent evolution. Involved rapid evolution of a large number of species from an ancestral group to occupy a variety of different ecological niches that may have become available suddenly.
Can arise in two different ways
evolution of a new structure, physiology or behaviour enabling exploitations of a different aspect of habitat
geographical isolation from competitors or predators
One form to another.
The transitional forms in the fossil record in response to natural selection
Involves the formation of many different species that are no longer closely related.
features similar in structure and origin but different in function. Similiarity in structure indicates common ancestry, while difference in function indicates adaption to different selection pressures in different environments. Can be seen in the limbs.
Structures with different evolutionary orignings that appear very similar because they carry out the same or similar functions.
The formation of new species resulting from populations becoming reproductively isolated; gene flow no longer occurs.
Speciation can occur:
gradually by the slow accumulation of small changes
instantly by the changes in chromosome number through polyploidy
Sympatric Species - are (closely) related species that live in the same geographic location.
Allopatric Species - are (closely) related species that live in different geographic location.
Reproductive Isolating Mechanism (RIM) - any factor that stops members of populations of the same spceices or members of different species from breeding together; it acts as a barrier to gene flow.
RIMS can be;
Prezygotic - act before the egg is fertilised
Postzygotic - act after the egg is fertlilised
Reproductive isolation may result from just one or a combination of prezygotic and/or postzygotic isolating mechanisms.
Geographical isolation results from physical barriers (rivers, mountains, oceans) separating populations. If the population come together again later, they are sufficiently different (as a result of selection pressures) that they do not/ unable to breed.
Results from the fact that the differences in structure of the external reproductive organs do not allow for the transfer of sperm between sexes.
Resutls from differences in habitat within the same geographical area, so that the populations rarely come in contact with each other.
Results from breeding behaviour occurring at different non-overlapping times. This can be saily or seasonal differences in timing of mating.
Results from differences in behaviour, typically mating behaviour such as courtship
Can also result from different activity patterns.
Results from the incompatibility of gametes. Sperm may not be able to fertlise an egg of another species because:
The egg’s surface does not have the correct chemical receptors
Sperm cannot penetrate the surface of the egg
Sperm cannot survive in the chemical environment of the female reproductive system
the zygote, embyo or offspring is inevitable so it dies early in its development
The hybrid reaches maturity but is infertile so it cannot breed
Occurs when the hybrid reaches maturity and is able to breed but the next generations are infertile or have reduced reproductive capability
Allopatric speciation is the process where speciation cannot occur until a population has divided into two or more geographically isolated populations.
Most common form of sympatric speciation is instant speciation. This involves the formation of polyploid therefore is more common in plants.
Less important that allopatric speciation
If populations become sympatric three things can happen:
Interbreeding
Populations do not hybridise
They hybridise freely and merges to form the original single species.
Through polyploid. Results in the evolution of many plant species. Results in a new species in a single generation due to the consequent formation of the postzygotic reproductive barrier of hybrid sterility.
Allopolyploidy is the more important of the two as it results in the hybrids containing the genes of two different species which can be advantageous to the polyploid should the selection pressures change.
Mountain building and changes in sea level