Unit 2 – Genetics and Adaptation
Evolution


All the species that exist today arose from earlier species by the
process of evolution – “descent with modification”
The scientists who developed the Theory of Evolution by Natural
Selection were Charles Darwin and Alfred Wallace
Natural Selection
 Natural Selection is the survival of those organisms best suited to
their environment
Process of Natural selection
 The main stages are as follows
o Organisms produce more offspring than the environment
o Members of a species show variation
o There is a struggle for existence, large numbers die – natural
selection
o Those best suited have a better chance for survival, those less
well suited die
o The survivors will reproduce and pass on their genes, some of
their offspring will carry the genes that helped them survive
Selection Pressure
 Is a factor which acts on individuals in a population
 Results in the death of some individuals and the survival of others
 An individual which is most likely to survive when a particular selection
pressure is applied is said to have a selective advantage
 The following diagram shows a model of natural selection
Mugwumps
Have the potential for an
Exceptional increase in population
Variation exists in the population
Selection pressures
predation
Possible selective advantage
Fast
(adaptations that suit survival) Runners
disease
competition temperature
Good
immune
system
Ability to
find food
Furry coats
Species
 A species is a group of organisms with similar genotypes and
phenotypes that usually only breed with each other and have access to
a common gene pool
 Species are not constant unchanging units, at any given time some
species will be relatively stable, some moving towards extinction and
others will be going through speciation
Speciation
 Speciation
o Is the formation of a new species
o Involves changes in genotype and phenotype that make the
organism more suited to the environment.
o Is brought about by evolution
The Mechanism
Isolation
A large interbreeding population may
become split into several sub-populations
by isolating barriers
Mutation
Causes new alleles to appear in each
population
Natural Selection
Selection pressures may be different in
different regions
So different populations will be
subjected to different selection
pressures. The gene pool will change
Different Species
Formed
After a very long time the changes in the
gene pool are so great that no
interbreeding is possible and no gene flow
will occur
Isolation Barriers
 The barriers which split populations, preventing interbreeding and
gene flow. They may not just be physical barriers
Geographical
Formation of geographical features that divide
populations e.g. sea, mountains
Ecological
Caused by changes in abiotic factors e.g. moisture
levels, pH of soil, temperature
Reproductive
Members of the population no longer able to breed with
each other
Gene Flow
Population
A




Population
B
Population
C
Population
D
This diagram represents one species which has been divided into
several populations
Populations that can breed together are
 A with B
 B with C
 C with D
Although A and C cannot breed together genes can move indirectly
through population B
If population B was removed then there would be two species
Adaptive Radiation
 Sometimes many species are formed form a single ancestral species
 Different selection pressures result in species that have different
adaptations from each other and from their common ancestor
 e.g. adaptive radiation in mammals
 Studies of anatomy show similarities that indicate they are related
 Structures like the limbs of mammals which have the same anatomy
are said to be homologous and have come from a common ancestor
 Structures which do the same thing but have arisen independently are
analagous.
High Speed Evolution
Evolution usually takes a very long time but there are organisms which can
show natural selection in action over a shorter time scale
Examples of high speed evolution
1.Peppered moth
 There are two forms of peppered moth
A light form – pale brown with black speckles
A dark form – black (melanic)
 The moths fly at night but during the day rest on trees
 Non-polluted areas
o The bark of trees is covered with plants called lichens
o A light moth is well camouflaged against lichen, the dark form is
more easily seen and is more likely to be eaten by predators
 Polluted areas
o Lichen is killed by high levels of sulphur dioxide and the bark on
trees is bare and covered in soot
o The dark form is well camouflaged against this background, the
light form is more easily seen and is more likely to be eaten by
predators
o
2.Antibiotic resistance in bacteria e.g. E Coli
 Each time an antibiotic, like penicillin, is used most but not all of the
bacteria present are killed
 The survivors have a genetic resistance to penicillin
 This trait is passed on to their offspring
 The population now contains a larger percentage of penicillin resistant
bacteria
 The frequency of resistant genes in the population has increased –
evolution has occurred.
 If enough changes a new species may form
Extinction of Species
 Occurs when the last individual of a species dies
 Extinctions have occurred continually since the origin of life on Earth,
once a species is extinct it can never reappear
 When species become extinct the niche they occupied becomes
vacant, as a result other organisms evolve and radiate out to fill these
‘spaces’
 Species may become extinct due to
o Habitat destruction

o Over hunting / fishing
At some times mass extinctions have occurred e.g dinosaurs. These
tend to be followed by a period of mass speciation
Conservation
 Human societies have caused large-scale disruption and degradation of
the enviroment
 Natural environments are rapidly being eliminated
 Pollution occurs in many areas
 Many plant and animal species cannot adapt to the rapid changes which
humans are causing in the environment and are facing extinction
 This decrease in biological diversity is alarming and much effort is
being put into saving some species - conservation
Importance of Conservation
 Species should be conserved as the genes they carry cannot be
replaced and may be important in the future.
 In human terms this genetic potential may provide future:
Food
Most food comes form just 20 species diseases may
threaten food supply
Fuel
Fossil fuels are running out alternatives are required
Raw Materials
Medicines
Agriculture
Fossil fuels are running out, alternatives are required for
the manufacture of plastics etc.
As new diseases evolve new treatments are required
Genes that make organisms more vigorous and resistant to
disease can be bred into stocks
Mechanism of Conservation
On-site
The creation of protected centres of diversity, wild life
reserves
Off-site
Captive breeding programmes
Where environments are being destroyed the organisms are
removed and bred in zoos with a view to returning them to the
wild
Gene banks – centres are set up to retain a store of genetic
material e.g. seed banks and rare breed farms
Artificial Selection
 Is the evolution of a wide variety of crops and domesticated animals
through selective breeding and hybridisation
 Humans have used domesticated plants and animals for many purposes
over thousands of years
Selective Breeding
 Breeders have selected those organisms which had desirable traits to
breed from
 This has resulted in many varieties
 Examples of organisms which have undergone artificial selection


Wild cabbage
Structure of plant
e.g. cauliflower, sprout, brocolli
Cattle
Milk yield – Jersey
Beef – Aberdeen Angus
Dogs
Herding ability – sheepdog
Sense of smell - Bloodhound
When selective breeding is used strains are formed by interbreeding –
mating of genetically similar individuals
As each generation is formed the strains have a higher degree of
homozygosity (many genes have identical alleles at each locus)
Hybridisation
 Crossing two different strains re-establishes heterozygosity (many
genes have two different alleles at each locus) and creates an F1
hybrid
 F1 hybrids are highly desirable as they show hybrid vigour – they are
bigger and more productive than either of their parents
 Many bedding plants and farm animals are F1 hybrids which although
very productive are not suitable for breeding as this would result in
very varied offspring
Genetic Engineering
 Artificial selection can be a very slow process, modern methods have
allowed faster changes to be brought about, by modifying the DNA of
an organism to insert new genes giving new characteristics

It is possible to isolate a DNA fragment containing a gene from one
organism and insert it into another
Locating Genes
 Genes can be located on a particular chromosome by
o Characteristic banding patterns on chromosomes, a gene can be
located by relating individual genes to particular bands
o Gene probes – a small “labelled” section of single stranded DNA
which will bind to a specific sequence of DNA
The Process of Genetic Engineering
Human DNA containing
desired gene
Endonuclease used to cut
gene from chromosome
Bacterial plasmid opened by
endonuclease
Gene sealed into plasmid
using ligase
Plasmid inserted into
bacterium and plasmid
multiplies
Bacterium multiplies and
gene is expressed
Product can be separated
and purified
Somatic Fusion
 Is used to overcome sexual incompatibility between plant species
o Unspecialised cells of two different plant species are selected
o The cells are treated with cellulase to remove the cell wall
resulting in protoplasts
o Protoplasts are fused to form a hybrid
o Division is induced and a callus forms
o Manipulation of hormone levels allows complete plant growth
 A plant is formed which combines good features of two different
species e.g. aphid resistance in potatoes / heavy yeild