2 Requirements for Evolution - 1) A source of variation between individuals of one species (can be
from mutations, crossing over, & independant assortment during cell division).
2) A change in the frequency of the genes in a gene pool of a population (due to natural selection).
Adaptive Radiatio...
IB Biology - Evolution (5.4 & Option D)
SL/HL Exam / Revised Questions and
Answers / Sure A+
2 Requirements for Evolution - 1) A source of variation between individuals of one species (can be
from mutations, crossing over, & independant assortment during cell division).
2) A change in the frequency of the genes in a gene pool of a population (due to natural selection).
Adaptive Radiation - The condition in which homologous structures are differentiated to perform
a variety of different functions.
- As speciation occurs, a particular structure may change to become adapted to a specific requirement
and carry out different functions.
(eg: Darwin's Galapogas Finches, & the pentadactyl limb)
Allele Frequency - The frequency of a particular allele as a proportion of all the alleles in a
population. (How common an allele is, in a typical interbreeding population).
Allele frequency can range from 0.0 to 1.0.
- Evolution always involves a change in allele frequency in a population's gene pool, over a number of
generations.
Allopatric Speciation - Occurs when members of a species migrate to a new area, forming a
population that is geographically isolated from the rest of the species. Therefore interbreeding becomes
impossible: GEOGRAPHICAL ISOLATION acts as a barrier between the gene pools of the populations (eg:
a mountain range, river etc). The populations can therefore split to form separate species. (eg: the lava
lizards of the Galápagos are separated into different species depending on the island which they live).
Allopolyploidy - Alloploids are polyploids with chromosomes derived from different species. It is
the result of doubling of chromosome number in an F1 hybrid (rare: a fertile hybrid).
- eg: Triticale, with 6 chromosome sets; 4 from wheat, and 2 from rye. The resulting species is infertile
with both parent species.
Analogous Characterstics - Structures which have a similar function but different evolutionary
origins. (Unrelated organisms with similar morphologies).
,Eg:
- The bird wing and the butterfly wing
- Dolphin fins and shark fins
- The wasp eye and the octopus eye
- The beetle leg and the cat leg
Ardipithecus ramidus (4.4 million years ago) - Only fragments of skulls and other bones have been
found so far. They suggest characters intermediate between chimpanzees and Australipithecus:
- Small numbers of large molars (like chimps)
- Incisors slightly smaller than those of chimps
- Canines blunt and projecting less than those of chimps
- Foramen magnum (hold through which the spinal cord enters the skull) further forward in apes,
suggesting Ardipethicus was at least partially bipedal.
Areas Which Favour Fossilisation - Areas where sediments are likely to be deposited over the
remains of organisms, protecting them from scavenger animals and from fungi and bacteria.
Artificial Classification - Artificial classification systems sometimes help with species identification,
but have no other value. An example of an artificial classification is putting insects, birds, and bats into
one group because they fly. The wings of these animals are an example of analogous structures (those
with a common function, but different evolutionary origin).
Assembly of Polymers - (eg: Polypeptides from amino acids)
- No oxygen in atmosphere meant that oxidation could not occur:resulting in a 'reducing atmosphere'.
- This would have made the joining of simple molecules to form more complex ones likely.
- Experiments have shown that it is possible to form organic molecules in a reducing atmosphere.
- This process is called POLYMERISATION and would allow the larger chemicals needed by cells to form.
Assumptions In Cladistics - - Changes in characteristics occur in lineages over time.
- Any group of organisms is related by descent from a common ancestor.
- There is a branching pattern of lineage-splitting (i.e: each branch will split into two groups)
, Assumptions Made When Using the Hardy-Weinberg Principle - When using this principle in
calculations, certain assumptions must be made:
- That there is random mating in the population
- That natural selection does not cause higher mortality of individuals with one allele than the other (no
directional selection)
- That there is no mutation
- That the population is large
- That there is no immigration or emigration
If these assumptions are correct, the population is said to be in Hardy-Weinberg equilibrium, and
therefore the equation is valid for that population.
Australopithecus afarensis (4 - 2.5 million years ago) - - Tall lower jaw
- Projecting face
- Fairly large molars
- Ape-like face (flat nose, no chin)
- Brain size similar to chimps
Australopithecus africanus (3 - <2.5 million years ago) - - Tall thick lower jaw
- Projecting face
- Large molars (for plant based diet)
- Bony strut
- Bipedal
- Small brain size
- Flatter face
Autopolyploidy - Autopolyploids are polyploids with multiple chromosome sets derived from a
single species. They usually have an odd number of sets of chromosomes, and are sterile. Autoploids can
arise from a spontaneous, naturally occuring genome DOUBLING (eg: potatoes). Others might form
following fusion of 2n gametes (unreduced gametes).
- Bananas and apples can be found as autotriploids.
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