Evolution 10.3 Gene Pools and speciation Flashcards
What is a gene pool?
consists of all the genes and their different alleles, present in an interbreeding population
How can multiple gene pools exist?
populations of same species can be geographically isolated
How can individuals contribute to the gene pool of the next generation?
reproduction
What is genetic equilibrium?
when all members of a population have an equal chance of contributing to the future gene pool
What is evolution?
the cumulative change in the heritable characteristics of a population overtime
Why can evolution occur?
mutations like new alleles, selection pressures favouring the reproduction of some varieties over others, barriers to gene flow between different populations
If a population is small, how can evolution additionally occur (cannot occur in large population)?
random events can also have a significant effect on allele frequency
What are selection pressures?
environmental factor that act selectively on certain phenotypes resulting in natural selection
What are the three patterns of natural selection?
stabilizing selection, disruptive selection, and directional selection
What occurs during stabilizing selection?
Selection pressures act to remove extreme varieties.
Individuals with the average form of a trait have the highest fit.
Give an example of stabilizing selection.
Human babies (too small ones are unable to defend themselves from infections and staying warm, too large ones are too large to deliver naturally)
What occurs during disruptive selection?
Selection pressures act to remove intermediate varieties, favouring the extremes
Individuals with either extreme variation have a greater fitness than individuals with the average trait.
What occurs during directional selection?
The population changes as one extreme of a range of variation is better adapted.
Individuals that display a more extreme form of a trait have a greater fit than individuals with an average form of the trait
What is speciation?
formation of a new species by the splitting of an existing population. They become reproductively isolated
When does speciation occur?
when various barriers isolate the gene pool of one population from tat of another.
What are the types of reproductive isolation?
Temporal (sympatric), Behavioural (sympatric), Geographic (allopatric)
What does reproductive isolation geographically mean?
Geographic separation of population where species come from same ancestor but because of different environmental pressures, need to adapt that causes them to evolve differently.
What does reproductive isolation behaviourly mean?
Sometimes isolation of gene pools occurs within the same geographical area.
When closely related individuals differ in their courtship behaviour, they are often only successful in attracting members of their own population
What does reproductive isolation temporarily mean?
For temporal isolation of gene pools in the same area, Populations may mate or flower at different season or different times of the day
In what ways can speciation occur?
abruptly or gradually due to divergence of isolated propulations
What is gradualism?
idea that species slowly change through a series of intermediate forms. Evolution occurred through long sequence of continuous intermediate forms
Why could gradualism not be completely true?
there was sometimes an absence of intermediate form in fossil records
What is punctuated equilibrium?
Long periods of relative stability in a species are “punctuated” by periods of rapid evolution
How could gaps in fossil record possibly not be gaps at all?
Punctuated equilibrium reasons that there was not no long sequence of intermediates.
What can lead to rapid speciation?
geographical isolation (allopatric speciation), opening of new niches within a shared geographic range
Where is rapid speciation common?
organisms with short generation times (prokaryotes/insects)
What are polyloid organisms?
more than two sets of homologous chromosomes
How do polyloids happen?
- Hyberdization event between different species
- Occurs when chromosomes duplicate in preparation for meiosis but then meiosis does not occur
- The result is a diploid gamete that when fused with a haploid gamete produces a fertile offspring.
- It has become reproductively isolated from the original population
- It can self -pollinate or mate with other polyploidy plants
- Can lead to sympatric speciation
Describe characteristics of polyploid?
polyploids may be well adapted to their environment;
common in plants / named example of speciation by polyploidy;
polyploidy is a form of sympatric speciation;
leading to reproductive isolation from parent species;
polyploid individuals can interbreed with one another;
A. named example (eg tomato, wheat, sugar beet, bagworm moth);
B. alteration of number of chromosomes (euploidy) / three (or more) sets of chromosomes;
C. larger nuclei / larger cells;
D. larger organisms / more vigorous; E. (generally) infertile;
F. alloploidy when of different species;
Outline example of a speciation through polyploidy
Alliun genus (onions, garlic and chives);
Determining species in the genus presents challenge to taxonomist as polyploidy are common within genus;
results in reproductive isolation (otherwise similar population)
reproduce asexually, polyploid gives advantage over diploidy under selection pressure;
What is an endemic species?
A geographically isolated species
What is the difference between analogous structures and homologous structures?
- homologous traits derive from common ancestors
- analogous traits developed from convergent evolution
What type of evidence is used to make a cladogram?
- DNA sequence
- amino acid sequence
- mitochondrial/chloroplast DNA
- shared characteristics
Why should a cladogram be constructed with more than one type of evidence?
- higher degree of certainty
- some could be misleading/anomalies
Why is mitochondrial DNA used to develop cladograms based on molecular clocks?
- Mitochondrial DNA sequences of genes are short, easy to examine
- mutations accumulate over time
- divergence is represented by amount of difference
- the greater the difference the earlier the divergence
Explain how mutations can be used as molecular clocks
- DNA base sequence/amino acid sequence differences result from mutations
- accumulate gradually over time
- constant rate is seen as molecular clock
- number of difference in sequence correlate to the time since species diverged from common ancester
