Transcript Evolution - MACscience

Evolution
An overview
DNA is made up of genes. A gene
is a short section of DNA which
carries the code for production of
one protein.
gene
Mutations
• Permanent change to the base sequence
of the DNA molecule.
• Can be caused by mutagens such as:
– Ionising radiation
– Chemicals
• Because mutations change the base
sequence, the coded message in the
genes change.
Remember: Mutations are only
inherited if they occur during
production of gametes.
sperm
egg
Nonsense mutation
Missense mutation
Insertion
Deletion
Frameshift
Duplication
Each protein has a distinct
structure.
Enzymes
Hormones
Structural proteins
Mutations can be harmful.
• Results in a phenotype that has poor fitness i.e
less able to compete for resources.
• Individuals with this phenotype either die before
producing offspring, or produce less offspring.
• This means that these individuals will be
‘selected against’ and the mutated gene will
eventually disappear from the gene pool.
Mutations can be beneficial
• These mutations result in a phenotype that
benefits the individual. i.e improves fitness.
• Individuals with this phenotype are better able to
compete for resources or avoid being eaten.
• This means that the new characteristic will be
‘selected for’ and over time the new phenotype
becomes more common in a population.
• They live longer and produce more offspring, so
the mutated gene becomes more common in the
gene pool.
Neutral mutations
• These mutations don’t result in any benefit
or harm to the individual under the current
environmental conditions.
• HOWEVER, if environmental conditions do
change, there might be an advantage in
having the mutated gene.
If the environment changes
• There will be ‘selection pressure’ favouring
those individuals with the phenotype that
allows them to survive and breed under
those new conditions.
• This process is called ‘natural selection’
i.e survival of the fittest.
• Over a long period of time a new species
may evolve.
A case study
Evolution of Probosidea – the
Elephant family
The Moeritherium is believed to be the
ancestor of elephants. They lived about
36 million years ago in Africa when the
earth was very warm and wet.
They were the
size of a pig
Moeritherium was adapted to a
tropical environment.
Over millions of years, the genes
coding for long trunks, tusks and
large size were selected for.
4 tusks
Gomphotherium lived from about 25 mya until 5 mya and
stood about 3 m tall.
The ancestors of modern elephants
spread out from Africa and adapted
to new environments.
Of course, the continents were in
different places millions of years ago.
Dinosaurs were wiped out by an asteroid impact.
Mammals evolved very quickly to
fill the niches left by the dinosaurs.
Ancestors of the modern elephant were
evolving at this time.
This period of time was warm even at the poles. Animals
were adapted to warm and moist conditions and plant
growth was prolific.
The ice ages
The sea level dropped and land bridges opened for animals
to migrate over.
During the ice ages, the northern
hemisphere vegetation changed.
summer
winter
Near the ice sheet tundra developed with
freezing winters and cool summers.
Further south, taiga vegetation
developed.
pine trees
Large size was selected for as it
insulated elephants against the cold
and protected them from predators.
Ambelodon
Smilodon was well adapted to
ambushing large herbivores.
Sabre
toothed cats
weighed
300kg
Giant ground
sloth
Mastodon lived in North America
from around 4 mya until 12 500 ya.
Weighed up
to 5 tonne
Mammoth migrated from Asia to
North America while sea levels
were low.
They lived from about 2 mya until 11 000 ya.
Mammoth were the successful end product
of millions of years of evolution. Huge size, a
woolly coat and massive tusks were an
advantage in a cold climate with large
predators.
Massive herbivores were preyed on
by massive carnivores.
Twice the size of a Grizzly
bear
Around 13 000 years ago the first
humans arrived in America.
The first people were expert hunters and used the most
sophistocated and lethal stone spear tips ever made.
The huge herbivores had not
evolved behaviours to cope with
human hunting.
Within a few thousand years all
huge herbivores and the predators
that fed on them were gone.
extinct
extinct
extinct
extinct
Meanwhile, Africa was still warm
and had become much drier.
Much of eastern and southern Africa became
grassland.
The modern African elephant evolved in this
environment. A number of traits were selected for.
Large size as protection from predators.
Lack of hair to prevent over-heating.
Big ears to radiate heat
Social behaviours
In Asia the Asian elephant had
evolved adaptations for a different
environment.
Summary
• Mutations result in genetic variety in a
species.
• Good mutations improve fitness and are
passed on to the next generation.
• If a group of animals migrate to a new
area or if environmental conditions
change, only the fittest survive.
• Eventually natural selection can result in
the evolution of new species.
The End