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 Chromosome Mutation

(one gene changes) (many genes are change)

e.g Albinism 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.