Download Variation and Evolution

Variation and Evolution
What is variation?
• Variation is when there are differences
between members of the same species.
Types of variation:
1) Inherited variation
2) Acquired variation
Inherited variation
• Inherited variations are caused by:
1) Sexual Reproduction
2) Mutations
Sexual Reproduction
• Sexual reproduction causes most genetic
variation:
1) Meiosis: the way in which chromosomes enter
a gamete at meiosis (law of Independent
Assortment).
Example: Human cell has 46 chromosomes. This
cell has 8 million different combinations of
chromosomes during meiosis.
Sexual Reproduction
• Sexual reproduction causes most genetic
variation:
2) At Fertilisation: each zygote represents at
least a 1 in 64 000 000 000 000 combination of
chromosomes.
Inherited Variation
Male Chromosomes
Female Chromosomes
Mutations
• Mutation also causes inherited variation.
What is a mutation:
• A mutation is a change in the amount or structure
of DNA.
• The correct protein is no longer produced
NOTE: The number of mutations that survive are very
low.
Mutations
• Most mutations (recessive allele) produce no
change in the characteristics of a diploid
organism. The dominant allele will still be
expressed.
• A small number of mutations can be beneficial
• Many mutations are harmful.
Mutations in a gamete
• This can be very serious
• Mutations may be inherited by the zygote and
passed onto all the cells in the child.
Examples of mutations
Causes of Mutations
Mutagens are agents that cause mutations.
Types of mutagens:
• X - rays, gamma rays, ultraviolet radiation
• Tobacco smoke
• Caffeine
• Preservatives
• Pesticides
Cigarette smoke caused mutations in
a gene called P53.
• Cigarette smoke caused mutations in a gene
called P53.
Smoking causing throat cancer
Throat cancer
Protecting against these mutations
• X –rays: wear a heavy lead shield to absorb x
ray
• UV rays – wear high sun protection factor
Types of Mutations
1) Gene Mutation (point mutation): Are
changes in a single gene
2) Chromosome mutation: are large changes in
the structure or number of chromosomes.
Gene Mutation
• Are changes in a single gene.
Examples of gene mutation:
1) Cystic Fibrosis (the inability to remove mucous
from lungs)
2) Haemophilia (inability to clot blood)
3) Albinism (lack of skin pigment)
4) Sickle cell anaemia
Gene Mutation
Sickle cell Anaemia
• This is an inherited blood disorder caused by a
mutation in the haemoglobin gene.
• Forms on a recessive allele
• 10 % of black africans have a single copy of this
mutation.
• 1% of black africans have a double copy
(homozgous recessive) and suffer from
disorder.
Sickle cell anaemia
Albinism
• Beautiful Albino Lion – YouTube
• Albino Animals - YouTube
Chromosome Mutations
• Are large changes in the structure or number
of chromosomes.
• In human somatic cells (non reproductive)
they have 46 chromosomes.
2n = 46
Examples of chromosome mutations:
• Down’s Syndrome: have one extra chromosome (2n = 47)
Summary of Mutations
Mutation
(sudden change in DNA)
Gene Mutation
(one gene changes)
e.g Albinism
Chromosome Mutation
(many genes are change)
e.g Down’s syndrome
Evolution
• Evolution is the way in which living things change
genetically to produce new forms of life over long
periods of time.
• Charles Darwin and Alfred Wallace have produced
the modern day view on evolution.
Galapagos Islands
On the Origin of Species by means of
Natural Selection
Theory of Natural Selection
Observation
Conclusion
1. Overbreeding
1. Struggle for existence
(competition)
2. Population numbers remain
constant
2. Natural Selection
3. Inherited variations occur in
population
Give an account of the Theory of Natural Selection. Name the
scientists who are associated with the theory and refer to any
one observation that prompted its development.
• A species produces a large number of offspring (high
reproductive rate). Trees produce thousands of seeds and
oysters produce million of eggs.
• The population of the organisms then remain constant due to
competition and the environment can no longer support them
any more.
• Some organisms show genetic variation because of sexual
reproduction (meiosis) or mutations.
Give an account of the Theory of Natural Selection. Name the
scientists who are associated with the theory and refer to any
one observation that prompted its development.
• The organisms that have variations may enable them to
adapt to their environment have a better chance of survival
(survival of fittest).
NOTE: unfavourable variations result in organism not surviving.
• The positive traits are then passed on to the next generation
who’s offspring survive, and those who do not have this
genetic variation may die out.
What is Natural Selection:
• It 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 following generations.
Richard Dawkins - Charles Darwin and Natural
Selection - YouTube
Evidence of evolution
1) Study of fossils
2) Comparative anatomy
3) Study of embryos
Evolution and fossils
Where humans came from:
Study of Fossils
• Palaeontology: study of fossils
Examples of fossils: bones, teeth, seed, foot
prints
Evolution of humans video
• Story Of Human Evolution (History Channel) YouTube
Fossil evidence for evolution
• Fossils can be aged (allows them to be
compared)
• Fossils discovered show changes when
compared to modern organisms.
• Modern fossils show increased complexity.
• Fossil evidence can be linked to environmental
changes.
Evolution of the horse
Evolution of the horse
• The ancestor of the modern horse developed
about 60 million years ago (size of the fox).
• 30 million years ago they were the size of a
large German shepherd.
• 15 million years ago they were the size of a
great dane.