Variation and Variation and EvolutionEvolution

Chapter 18Pg – 196-204

ObjectivesObjectives

At the end of this lesson you should be able to:  1.Define variation and mutation2.List the causes of variations and mutations3.List the types of mutations4.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 VariationInherited Variationb) Inherited variation is caused

by caused by sexual reproduction and by mutations.

Inherited VariationInherited 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

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

FACT

Whose Child?

Parents & Children

Offspring are similar to their parents but are not identical

Cause – crossing over

Differences between parents and offspring

Crossing OverCrossing Over

Fusion of gametesFusion of gametes

Sperm and egg cell fuse to form a zygote

The combination of chromosomes leads to great variation in species

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?

Learning Check

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 anaemia2. Cystic Fibrosis (inabilityto remove mucus from thelungs)3. Albanism (lack of pigment melanin)

Sickle Cell AnaemiaInherited blood disorderCaused by mutation in the haemoglobin

geneA 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 transfusionsLocation: Southern Europeans & North

Africans

Chromosome mutationsChromosome 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.

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.

Chromosome Number Variations

Downs SyndromeDowns Syndrome

Dying for a SuntanDying for a SuntanSunlight 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.

SmokingSmokingA chemical in cigarette smoke

causes mutations in a crucial gene associated with cancer.

Cigarette smoke caused mutations in a gene called P53.

Learning CheckLearning Check

1. What is meant by aneuploidy?

2. Give an example?

3. 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 learnedWhat have you learned

Can you ……………… 1.Define variation and mutation2.List the causes of variations and

mutations3.List the types of mutations4.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 SelectionNatural 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 EvolutionComes from three main areas:1. Study of fossils2. 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 veryprecisely. About 98% of the organismsthat ever lived have gone extinct.

Comparative anatomy – vertebrate limbs

Embryos and evolutionary history

DNA Evidence

Example of EvolutionEvolution of the horse

Fossil record of modern horse is very well documentedCovers 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 Miohippus

Neohipparion Equus