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Part 11: Evolution
1. Evolution: Descent with modification; changes in the gene pool of a population
over time; the idea that living species are descendants of ancestral species that
were different from the present-day ones; also defined more narrowly as the
change in the genetic composition of a population from generation to generation.
 Divergent Evolution: the process whereby organisms that have different
adaptations from their recent ancestors survive in changed habitats; or, the
process whereby organisms with a recent common ancestor develop
different adaptations in different habitats. (Ex. Darker coloured moths
survived a highly polluted area where the trees darkened while white moths
died out).
 Convergent Evolution: Species evolve from different origins but under
similar environmental conditions to have similar traits. (ex. Aardvarks and
anteaters)
*The following are different pieces of evidence that support the theory of
evolution:
 Palaeontology: the study of fossils; through fossils, many similarities of
extinct organisms have been found in relation to modern day organisms.
 Biogeography: the study of the distribution of plants and animals in the
environment; similar animals show up in different places all over the world,
in places where they’d never come in contact with each other. Evolution
from a common ancestor would lead to these similar characteristics, as they
would evolutionize differently in different environments.
 Embryology: the study of the development of an organism; many embryos in
early development are almost identical to very different species.
 Comparative Anatomy: the study of the anatomy of various animals; many
animals have similarities in structures and functions of their anatomy:
o Homologous Structures: features of animals that are structurally
similar but functionally different. (ex. a whales fin to a birds wing to a
human arm)
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o Analogous Structures: features of animals that are functionally similar
but structurally different. (ex. the eyes of scallops, insects and
humans).
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 Molecular Biology: The branch of biology that deals with the structure and
function of the macromolecules (e.g., proteins and nucleic acids) essential to
life; similarities can be found between species in their genomes.
2. Natural Selection: A process in which individuals that have certain inherited
traits tend to survive and reproduce at higher rates than other individuals because
of those traits.
 Directional Selection: directional selection occurs when natural selection
favours a single phenotype and therefore allele frequency continuously shifts
in one direction. (ex. brown beetles living in mud will outlive green beetles
living in mud).
 Stabilizing Selection: a type of natural selection in which genetic diversity
decreases as the population stabilizes on a particular trait value; Mode of
natural selection by which intermediate phenotypes in the range of variation
are favoured and extremes at both ends are eliminated.
 Disruptive Selection: describes changes in population genetics in which
extreme values for a trait are favoured over intermediate values.
3. Charles Darwin: a 19th century British naturalist who sailed across the world on
the HMS Beagle. Darwin developed the theories of evolution and natural selection
while studying organisms in the Galapagos Islands. Darwin concluded that:
 Each species produces more offspring than can survive
 These offspring compete with one another for available resources
 Organisms of the same species from different populations vary
 The offspring with the most favourable traits are more likely to survive and
produce more offspring
4. Jean-Baptiste de Lamarck: 18th century theorist who proposed that organisms
only have traits for a purpose (use it or lose it). For example, tortoises that he
observed had long necks as they had to reach higher for leaves to eat.
5. Genetic Variability: differences between individuals of the same species. This is
caused by random mutations of selection.
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6. Speciation: the emergence of new species after the process of evolution; when a
species has evolutionized to the point that its new characteristics are different
enough for it to be considered a different species.
 Allopatric Speciation: when a new species develops due to geographical
separation. Commonly separated by water (ie. sea, lake) or mountains.
 Sympatric Speciation: when a new species develops without any
geographical separation. Common in plants.
7. Hardy-Weinberg Law of Equilibrium: this law states that a population will be in
genetic equilibrium if it meets five specific conditions: (1)Large population; (2)No
mutations; (3)No In of Out [no immigration or emigration]; (4)No sexual selection
[random mating]; (5)No natural selection. In other words, the theory is impossible,
although it does have some functions. There are two formulas with the HardyWeinberg theories (where p and q represent opposite alleles or genotypes):
 Allele Frequency Formula (p + q = 1): using this formula, you can find the
frequency of one allele once give the other. (Ex. if allele R is 0.7, then allele r
must be 0.3 because 0.7 + 0.3 = 1)
 Genotype Frequency Formula (p2 + 2pq + q2 = 1): in this equation, p2
represents the homozygous dominants, 2pq represents the heterozygous,
and q2 represents the homozygous recessive. You can pair this formula with
the first to answer questions about allele frequencies.
o Example 1: 16% of a fruit fly population as green eyes (recessive trait).
What is the allele frequency for red eyed flies?
Because q2 is used for homozygous recessive, we say:
q2 = 0.16
q = 0.4 (Allele frequency for green eyes)
We now plug this in to find the other allele frequency.
q+p=1
0.4 + p = 1
p = 1 – 0.4
p = 0.6
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o Example 2: 9% of the fruit flies have green eyes (recessive trait), 49%
are homozygous for red eyes. How many are heterozygous (%)?
We first find p and q, then plug that into 2pq (which represents
the heterozygous).
Note: the
p2 = 0.09
q2 = 0.49
percentages
p = 0.3
q = 0.7
all add up to
Plug it in: 2pq = % of heterozygous [2 x 0.3 x 0.7] = 42% 100%!
8. Genetic Drift: when the alleles of a gene pool change as on of the HardyWeinberg conditions is not met.
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