10.3 Gene pools and speciation Flashcards
What is a gene pool?
All of the genes and their different alleles, present in an interbreeding population
What does a large and small gene pool indicate?
Large: high amounts of genetic diversity, increasing the chances of biological fitness and survival, more genetic variation
Small: low amounts of genetic diversity, reducing biological fitness and increasing chances of extinction, more likely to inherit mutations
What is genetic equilibrium?
When all members of a population have an equal chance of contributing to the gene pool
* individuals that reproduce contribute to the gene pool of the next generation
What are 4 ways evolution can occur?
- Mutations - random changes to the structure of DNA introducing new alleles
- Selection pressures favouring the reporoduction of some varieties over others
- Gene flow (movement of alleles between population) emerging between different populations
- Genetic drift - changes in gene pool due to a chance/random event e.g. trampling/hunting
What is the impact of random events on a small population?
A significant effect
What does evolution require of in populations to do over time?
Evolution requires that allele frquencies change with time in populations
* Gene pools can be used to determine allele frquency - the proportion of a particular allele within a population
What does evolution require of in populations to do over time?
Evolution requires that allele frquencies change with time in populations
* Gene pools can be used to determine allele frquency - the proportion of a particular allele within a population
What are the 3 main types/patterns of natural selection?
- Stabilising
- Directional
- Disruptive
What happens in stabilizing selection?
- Selection pressures act to remove extreme varieties
- Bell shape graph - normal distribution
- Natural selection that favours the average/intermediate phenotypes (positive selection) and extreme phenotypes are selected against (negative selection) and may be removed from gene pool all together
- Reducing genetic variation
- Occurs when the environment is stable
What happens in disruptive selection?
- Selection pressures act to remove intermediate varieties, favouring the extremes
- Opposite extreme traits are favoured, average trait is eliminated
- Extreme phenotypes are favoured (positive selectional) and average/intermediate phenotype is selected against (negative selection)
- Relatively rare
- Occurs when there are fluctuations in the environmental conditions e.g. seasons
What happens in directional selection?
- the population changes as one extreme of a range of variation is better adapted
- Natural selection where an environmental change gradually favours a new phenotype (e.g. peppered moths)
- Occurs when there is a gradual change in the environment
What is speciation?
The formation of a new species by the splitting of an existing population
What are two main types of isolating mechanisms that can cause speciation?
- Geographical separation aka allopatric speciation
- Reproductive aka sympatric speciation
What is allopatric speciation?
The formation of two diferent species from one original species, due to geographical isolation
* populations are separated by geographical features such as lackes, rivers, oceans and mountains
* There is a barrier to gene flow between the populations
* The isolated populations are subjected to different selection pressures in two different environments so undergo independent changes to the allele frequencies within their gene pools as a reult of mutation, selection and genetic drift
What is sympatric speciation?
The formation of two different species from one original species, due to reproductive isolation, while the population inhabit the same geographical location
* More common in plants than in animals
* Can be due to genetic changes e.g. change in chromosome number or mutation
-> Changes in flower structure
-> Changes in courtship behaviour
What are two types of sympatric isolation?
Temporal and behavioural
What is temporal sympatric isolation?
Populations may mate or flower at different seasons or different tymes of the day
What is behavioural sympatric isolation?
When closely related individuals differ in their courtship behaviour, they are often only successful in attracting members of their own population
Do populations have the same allele frequencies?
Different populations have different allele frequencies
What are the two theories about the pace of evolutionary change?
- Gradualism
- Punctuated equilibrium
What is gradualism?
It is the idea that species slowly change through a series of intermediate forms
Gradualism predicted that evolution occured by a long sequence of continuous intermediate forms. The absence of these intermediate forms was explained as imperfections in the fossil record
What was gradualism confronted by? What was explained about it?
It was confronted by gaps in the fossil record i.e. an absence of intermediate forms
The absence of these intermediate forms was explained as imperfections in the fossil record
What is punctuated equilibrium?
The idea that long periods of relative stability in a species are punctuated by periods of rapid evolution
According to the theory of punctuated equilibrium, what do the gaps in the fossil record show?
- It might not be gaps at all, as there was no long sequence of intermediate forms
- Events such as geographic isolation (allopatric speciation) and the opening of new niches within a shared geographic range can lead to rapid speciation
- Rapid change is much more common in organisms with short generation times like prokaryotes and insects
What is polyploidy?
- When an organism has more than two sets of homologous chromosomes
- A common source of reproductive speciation
- Has more chromosomes than they should have
- Occur more commonly in plants, though it does also occur in less complex animals
What can polyploidy result from?
Hybridisation events between different species
How can polyploids who’s chromosomes originate from the same ancestral species occur?
- When chromosomes duplicate in preparation for meiosis but then meiosis doesn’t occur. The result is a diploid gamete that when fused with a haploid gamete produces a fertile offspring.
- In other words, the polyploid has now become reproductively isolated from the original population
What can polyploid plant mate with?
It can self pollinate or it can mate with other polyploid plants
What speciation can polyploid lead to?
Sympatric speciation
What are does the Allium genus include?
Onions, leeks, garlic and chives
How do Allium reproduce?
Asexually
How might polyploidy help?
- May confer an advantage over diploidy under certain selection pressures
- Can be used for human benefit e.g. agriculture, food production
