Gene pools and speciations Flashcards
1
Q
What is a gene pool and population?
A
- Total of alleles (variations of genes) for all genes present in an interbreeding population
- Population: individuals of the same species living in the same place and time
2
Q
What determines a large gene pool? What is allele frequency?
A
- High amounts of genetic diversity, increasing the chances of biological fitness and survival
- Allele frequency: measures how common an allele is in a population
- The depth of the gene pool is measured by the no. of alleles and their relative frequencies
3
Q
What needs to change with time in a population for evolution and why?
A
- For evolution to occur, the allele frequencies need to change within the gene pool of the population
- These changes in heritable characteristics are needed across generations
4
Q
What are 5 processes that affect the allele frequencies in a gene pool?
A
- Mutations: random change in genetic composition, due to changes in DNA base sequences
- Gene flow: movement of alleles into or out of a population (immigration, emigration)
- Reproduction: new gene combinations, alter allele frequencies
- Genetic drift: as result of random event (external)
- Natural selection: environmental pressures
5
Q
What is selective pressure? What are the three types of selection?
A
- Environmental factors affect the rates of survival of certain phenotypes
- Directional, stabilizing and disruptive selection
6
Q
Explain stabilising selection.
A
- Intermediate phenotypes are favoured
- The extreme phenotypes are not suitable
- Occurs when environmental conditions are stable, lack of competition
- Phenotypic distribution clusters in centre
- E.g. length of a tail (intermediate length favoured)
7
Q
Explain directional selection.
A
- When one extreme phenotype is favoured and the other is rejected
- Causes phenotypic distribution to shift to one direction (towards beneficial extreme)
- Gradual changes in environmental conditions
- E.g. antibiotic resistance of bacteria
8
Q
Explain disruptive selection.
A
- When both phenotypic extremes are favoured, intermediate is rejected
- Phenotypic distribution deviates in the centre, bimodal spread
- Fluctuating environmental conditions, favours two different phenotypes
- Continued separation of population lead to speciation
9
Q
What is reproductive isolation?
A
- The failure of individuals from two populations to mate and produce fertile offspring, results in the reduction or elimination of gene flow between the populations
10
Q
How does reproductive isolation occur?
A
- When barriers prevent two populations from interbreeding, keeping the gene pools separate which can lead to speciation
11
Q
What are three ways a population can become reproductively isolated?
A
- Geographical isolation
- Behavioural isolation
- Temporal isolation
12
Q
Explain geographical isolation.
A
- Occurs when two populations occupy different habitats within a common region or due to a physical barrier
- E.g. lions and tigers could interbreed by occupy different habitats
13
Q
Explain behavioural isolation.
A
- Occurs when genetically-influenced differences in behaviour reduce or prevent mating between two parts of a population
- E.g. production of a mating song in male crickets
- These behavioural differences can be bird dances, mating sites or mating songs
14
Q
Explain temporal isolation.
A
- When two populations differ in their periods of activity or reproductive cycles
- E.g. leopard frogs and wood frogs reach sexual maturity at different times in the spring, don’t interbreed
15
Q
What is speciation and when does it occur?
A
- Evolutionary process that results in the formation of a new species from pre-existing species
- Occurs when reproductive isolating mechanisms prevent two breeding organisms from producing fertile offspring
16
Q
What are the two types of speciation?
A
- Allopatric speciation (geographical)
- Sympatric speciation (reproductive)
17
Q
What is allopatric speciation?
A
- When a new species develops as a result of a part of a population becoming geographically isolated from others
- The populations evolve separately and reach a degree of genetic divergence, can no longer interbreed
18
Q
What is sympatric speciation?
A
- When a different species develops in the same geographic area due to behavioural, temporal or other forms of speciation.
- Isolation due genetic abnormalities, chromosomal error
19
Q
What is polyploidy? When will speciation occur?
A
- The presence of more than two complete sets of chromosomes in a cell, (diploid instead of haploid)
- This is a non-disjunction, meiotic cell fails to undergo cytokinesis, chromosome number will double
- Offspring has additional sets of chromosomes (polyploidy)
- Speciation will occur when the polyploid offspring is fertile but cannot interbreed with the original parent population
20
Q
What happens when a triploid and diploid individual reproduce?
A
- The offspring will also be triploid and usually sterile (uneven number of chromosomes)
21
Q
Why are polyploid crops desirable to farmers?
A
- Occurs by self-pollination and asexual reproduction, more common in plants
- It allows the production of seedless fruits, since they are infertile
- AND the crops typically grow larger and demonstrate improved disease resistance
- E.g. seedless watermelons are triploid
22
Q
What is hybrid vigour?
A
- When the hybrid exhibits traits that are more desirable than either parent
- Often case in polyploidy
23
Q
Explain the speciation in allium.
A
- Allium is a genus involving monocotyledon flowering plants e.g. onions, garlic, chives, leeks
- In these species polyploidy occured, resulted in reproductively isolated populations
24
Q
What are two paces of speciation?
A
- Gradually (divergence of isolated populations) or punctuated equilibrium
25
Q
Explain gradualism.
A
- Speciation occurs uniformly, by gradual transformations of whole lineages
- Continuous process, big changes result from many small continuous changes
- E.g. immigration, introduction of new gene pool
- Generally adaptations for better survival too
26
Q
Explain punctuated equilibrium.
A
- Species remain stable for long periods before undergoing abrupt and rapid change (rapid burst of phenotypic change)
- Periodic process, big changes occur suddenly, followed by long periods of no change
- Often lack of transitional fossil evidence
27
Q
What is genetic drift?
A
- Change in the composition of a gene pool as as result of chance or random events
- Occur faster in smaller populations, chance events will have a bigger impact on the gene pool
- Unstable allele frequencies, low genetic drift
28
Q
What are allele frequencies?
A
- Percentage or proportion how frequently an allele from a specific gene locus occurs in a population
29
Q
How do you compare the allele frequencies of geographically isolated populations?
A
- Two types: ancestral and derived alleles
- Identify regions where the ancestral allele is the only one present
- Identify in how many regions the derived allele is present
- The population with the greatest percentage of the derived allele
30
Q
What is genotype frequency?
A
- Number of individuals with a given genotype as proportion of the entire population
31
Q
What are the equations for allele frequency and genotype frequency?
A
Allele frequency: p+q=1
Genotype frequency: p2+2pq+q2=1
