Transcript Variation and Evolution

Variation and Evolution
Chapter 18
Pg – 196-204
Objectives
At the end of this lesson you should be able
to:
1.
2.
3.
4.
Define variation and mutation
List the causes of variations and mutations
List the types of mutations
Discuss the causes for and effects of
increased mutation rates
Variation means there are differences
between the members of a species.
How would members of a species differ?
There are two types of variation
a)
Acquired variation is learned during life.
Examples of acquired conditions in
humans are:
 language
obesity
 athletic skills
mental skills
 body building
sun tan

Inherited Variation

b) Inherited variation is caused by caused
by sexual reproduction and by mutations.
Inherited Variation
Identical twins who were raised apart, Roger (left) and
Tony first met at twenty-five and discovered they had
many similarities. Photograph by Nancy
Causes of Inherited Variations
1.
Sexual reproduction
2.
Mutations
FACT
When your parents cells undergo meiosis to
produce sperm/egg cells
8 million different combinations of their
chromosomes are possible
Every zygote is a 1 in 64,000,000,000,000
combination of chromosomes!
This leads to great variation in species
Whose Child?
Parents & Children
Differences between parents and offspring

Offspring are similar to their parents but are
not identical

Cause – crossing over
Crossing Over
Fusion of gametes
Sperm and egg cell fuse
to form a zygote
The combination of
chromosomes leads to
great variation in species
Learning Check
1.
What happens during meiosis?
2.
What does meiosis lead to?
3.
What are the causes of variation?
4.
Why are offspring not identical to their
parents?
A mutation is a change in the amount or
structure of DNA.
Mutations can be either good, bad or have no effect at all.
A good mutation can help an organism survive in a particular
environment e.g. a mutation that causes better eyesight. This mutation
will probably be passed onto offspring and help them survive also.
Individuals without this mutation may not survive as well in the habitat
and may eventually die out.
Eventually all of the members of the species will have this mutation.
Causes of mutations:
Mutations can occur naturally
(spontaneous) or can be caused by
mutagens.
Mutagens are agents that cause mutations
e.g. some types of radiation and some chemicals.
Examples:
Ionizing radiation such as x-rays, gamma rays,
cosmic rays and ultra violet (UV) radiation.
Chemicals such as formaldehyde, tobacco smoke,
caffine, many drugs, pesticides and preservatives.
Types of Mutations
A gene (or point) mutation is a tiny
change in a single gene (often it only involves a
single incorrect base).
Examples:
1.Sickle cell anaemia
2. Cystic Fibrosis (inability
to remove mucus from the
lungs)
3. Albanism
(lack of pigment melanin)
Sickle Cell Anaemia
Inherited blood disorder
Caused by mutation in the haemoglobin
gene
A person with two recessive copies of the
recessive allele produces haemoglobin
with one incorrect amino acid. This
results in an insoluble form of
haemoglobin that causes the red blood
cells to be sickle (curved) shape.
This causes red blood cells to clump and
get trapped in smaller blood vessels
Symptoms: paleness, weakness, heart
failure severe pains, damage to brain &
other organs and often death.
Treatment: Blood transfusions
Location: Southern Europeans & North
Africans
Chromosome mutations
Chromosome mutations are larger changes in
the structure or number of one or more
chromosomes.
e.g. Down’s syndrome is caused by three number
21 chromosomes.
The extra chromosome comes from the mother.
It causes too much of a brain enzyme to be
produced and causes the brain to form
incorrectly.
Chromosome Number Variations

Except for the X and Y, humans don’t
survive with only 1 copy of any
chromosome. Also, 3 copies is lethal in
most cases.
Downs Syndrome
Dying for a Suntan
Sunlight contains UV radiation (the component
that causes a suntan)
This can cause an abnormal cross link in DNA to
form between certain adjacent bases.
In most normal cases the cells can repair this
damage, but sometimes a mutation can occur
Unprotected exposure to UV radiation by the
human skin can lead to skin cancer and extensive
skin tumors.
Smoking

A chemical in cigarette smoke causes
mutations in a crucial gene associated
with cancer.

Cigarette smoke caused mutations in a
gene called P53.
Learning Check
1.
2.
3.
What is meant by aneuploidy?
Give an example?
What are the causes of structural variation
in chromosomes?
4.
Give an example of a structural variation?
5.
What are the causes of mutations?
What have you learned
Can you ………………
1.
2.
3.
4.
Define variation and mutation
List the causes of variations and
mutations
List the types of mutations
Discuss the causes for and effects of
increased mutation rates
Evolution
Evolution is the way in which living things
change genetically to produce new forms
of life over long periods of time.
Outline of the Theory of Natural Selection
H.M.S. Beagle Voyage
HMS Beagle made three voyages of exploration.
1826 - 1830: Leaves Plymouth on 22 May for first surveying voyage to
Tierra del Fuego, South America.
1831 - 1832: Darwin joined the second voyage to South America and then
around the world.
1837 - 1843: Third surveying voyage to Australia
In the Galapagos Islands Darwin noticed how the same species of birds,
cut off from centuries on different islands, had developed in quite different
ways. This and many other amazing discoveries
Interesting Information
Charles Darwin was born in England on the 12th of February 1809,
he died on the 19th of April 1882.
He is most famous for his work on natural selection, the idea that all
species of life have evolved over time from common ancestors. This
process involves favorable traits becoming more common in
successive generations of living things while at the same time
unfavorable traits become less common.
Not only did Darwin develop the idea of natural selection, he also
presented compelling evidence from his detailed research which
included a five year voyage on the HMS Beagle. On this voyage,
Darwin visited ecologically diverse regions such as Brazil, Chile,
Australia, the Falkland Islands and the Galapagos Islands.
His 1859 book ‘On the Origin of Species’, detailed much of his
research on natural selection, it contained a large amount of evidence
to back up his ideas and became a landmark work in the field of
evolutionary biology.
Darwin’s ideas created a lot of discussion regarding the impact on
various scientific, religious and philosophical viewpoints.
Natural Selection
Natural Selection is the process by which
those organisms with genetically
controlled characteristics that allow them
to be well adapted to their environment
will survive and reproduce to pass on
their genes to the following generations.
e.g. wolves & rabbits
Evidence for Evolution
Comes from three main areas:
1. Study of fossils
2. Comparative anatomy (comparing
structure of different organisms)
3. Study of embyros
(4. DNA evidence – not on syllabus)
We only need to study one of the above
Paleontology is the study of fossils.
Fossils are generally rocks that have kept
the shape of an organism.
Fossils can be aged very
precisely.
About 98% of the organisms
that ever lived have gone extinct.
Comparative anatomy – vertebrate limbs
Embryos and evolutionary history
DNA Evidence
Example of Evolution
Evolution of the horse
Fossil record of modern horse is very well
documented
Covers a times pan of about 60 million
years and involves many hundreds of species
most of which are now extinct.
Many trends have been noted in the
evolution of the horse and we will look at
one change: the height of the animal.
Ancestor of modern horse developed 60
million years ago. They were about the
height of a fox (0.4m)
Fossils from about 30 million yeas ago show
that ancestors of the horse were larger
about the size of a German Shepherd dog
(0.6m)
Fossils about 15 million years ago show the
existence of a creature that was about
the size of a Great Dane dog (1m)
The modern horse evolved 1 million years
ago and is normally (1.6m)
Hyracotherium
Neohipparion
Miohippus
Equus