Option D - Evolution (D2)
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Describe at least three examples of barriers between gene pools
- 1.Temporal (time) isolation (pollinate at different times)
- 2.Geographical isolation (separated by a river etc)
- 3.Behavioural isolation (plumage, song, courting ritual needs to be appropriate)
- 4.Ecological isolation (same species live in different habitats)
- 5.Mechanical isolation (genitalia don't fit!)
How does polyploidy occur?
By non-disjunction (in meiosis)
Formation of a new species
What are the two versions of polyploidy?
What is autopolyploidy?
Are polyploids with multiple chromosome sets derived from the same species. Form after fusion of 2n gametes.
What is allopolyploidy?
- When two species come together to form a hybrid...but the hybrid is sterile because of an odd number of chromosomes until the doubling of the chromosomes.
- e.g. Triticum turgidum (wheat) fuses with Secale cereale (rye). It makes Triticale which is fertile.
What is allopatric speciation?
- When a species is subject to geographic isolation.
- (Even when barrier is removed, the species may not be able to interbreed).
What is sympatric speciation?
Two varieties of a species in same geographic area that do not interbreed, and so speciation occurs. e.g. apple maggot fly that breeds on two fruit trees that ripen at different times. This is temporal isolation.
What is adaptive radiation?
When many species evolve from a single species (very rapidly). Happens when species are able to exploit different environmental niches in different ways.
What is convergent evolution?
Acquisition of same biological trait in unrelated organisms
What is divergent evolution?
When two similar species start to evolve in different ways. When the 'split' occurs, it may result in adaptive radiation.
Features that come about as convergent evolution are known as...?
Features that come about as divergent evolution are known as...?
Examples of analogous structures are
- wings in birds, bats, insects
- eyes in squid, humans
- echolocation in bats, whales, shrews
Examples of homologous structures are
- pentadactyl limb
- Darwin's finches beaks
What is gradualism?
The theory that changes in species are small, continuous and slow
What is punctuated equilibrium?
The theory that changes in species occur (relatively) quickly, followed by long periods of no change
When did gradualism originate?
In early 18th Century by Darwin
When did punctuated equilibrium originate?
In late 20th Century
Give one example of transient polymorphism
Biston betularia Peppered moth. Over a short period of time it evolved to a dark form (industrial melanism) in industrial revolution. In cleaner air act of 1956, it reverted to a pale form.
Give one example of balanced polymorphism?
Sickle cell anemia
What is balanced polymorphism?
When two or more alleles within a population are stabilized by natural selection. It is maintained by two selective pressures.
What is a gene pool?
All the genes within an interbreeding population.
What is allele frequency?
the frequency of an allele, as a proportion of all alleles of the gene in the population.
What is a species?
This is a tricky one to answer! There are many ways to answer.
- Normally is defined as having
- •Similar physiological and morphological characteristics that can be observed and measured
- •Have the ability to interbreed and produce fertile offspring
- •Genetically distinct from other species
- •Have a common phylogeny
- BUT CONSIDER
- •individuals that could breed but don't because of some kind of isolation
- •or organisms that breed asexually not sexually
- •or infertile organisms
- •fossil remains can't tell if species were able to interbreed!
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