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Genetic changes in populations that over time, lead to new organisms. e.g species
A group of organims that can interbreed to produce viable offspring
A local interbreeding population of speices. Each deme will be fully or partially isolated from other demes.
A gradual change of species over a geographical gradient. A series of demes along an environmental gradient
The process where one or more species is formed from an existing species.
Formation of a species that are geographically seperated from one another.
Allopatric Speciation Process ( _ Steps)
- 6 Steps
- 1. Two populations seperate
- 2. Gene flow stops
- 3. Differences in environment mean that natural selection acts differently in the two populations. Individuals best suited to the environemnt will produce more offsping leading to evolutionary changes.
- 4. Over time, the populations become genetically and phenotypically different.
- 5. If enough time passes, the populations become so different they are no longer able to interbreed and produce offspring = two new species.
- 6. If the populations are still able to interbreed with each other, they may be classes as sub-species.
When species arise without geographical seperation.
Where a new species suddenly arises. e.g. Polyploidy
Where one group of individuals in a population adopt a new lifestyle and only breed with individuals who adopt this lifestye.
Having three or more complete sets of chromosomes.
The failure of chromosomes or chromatids from seperating into different cells during meiosis.
The doubling of chromosomes in a hybrid which means chromosomes can now pair up and the hybrid is now fertile. Also known as somatic doubling.
Polyploidy individual resulting from individuals of the same species.
Polyploidy individual resulting from individuals of different species.
What are the major advantages of polyploids?
Bigger, sterile if uneven number of chromosomes. Allopolyploid combines the characteristics of two species.
Reproductive Isolating Mechanisms. (2 Types)
Barriers that prevent species from interbreeding. Prezygotic and Postzygotic
Prezygotic Reproductive Isolative Mechanism (4 types)
Barriers that prevent a zygote forming as offsping. Temporal, Behavioural, Structural and Gamete Incompatibility.
Barrier to gene flow such as breeding at different times of the year that prevents interbreeding of closely related species.
Barriers to gene flow such as different courtship displays that prevent interbreeding of closely related species.
Barrier to gene flow such as differences in reproductive organs that prevents interbreeding of closely related species.
Barrier to gene flow where the sperm or egg of the two species differ, preventing fertilisation from occuring. This prevents interbreeding between closely related species.
Postzygotic Reproductive Isolating Mechanism (4 types)
Barriers that prevent the zygote developing to form fertile, healthy offspring. Hybrid Inviability, Hybrid Sterility, Hybbrid Disadvantage, Hybrid Breakdown.
A zygote is produced but does not develop properly and dies.
A zygote is produced but the hybrid produced is sterile so cannot produce offspring. E.g mule
A zygote is produced and the hybrid may be feritle but has lower fertilliy and is not well adapted to the environment
The hybrid offspring is fertile but produce infertile or non-viable offspring
Different Patterns of Evolution ( _ Types)
- 1. Divergent Evolution
- 2. Convergent Evolution
- 3. Co- Evolution
- 4. Punctuated Equilibrium
- 5. Gradualism
Exchanging of alleles between populations through immigration and emigration