VARIATION AND EVOLUTION

Variation

There are different characteristics with many intermediates in between.

E.g. height, weight, skin colour …etc

Caused by different genes as well as different environment.

There are different characteristics with no intermediates in between.

E.g. blood types, eye colour…etc

Caused by different genes

Continuous variation Discontinuous variation

Diagrams representing variation

Continuous

variation

histogram

Diagrams representing variation

Discontinuous variation

Bar chart, bars seperated

Count the number of tongue rollers and non tongue rollers in class.

What type of variation does this characteristic show?

Can you tell what causes this type of variation?

Can you find out which characteristic is dominant?

Tongue roller or not?

Tongue roller Non tongue roller

Mutation

A sudden unpredictable change in genes or chromosomes of an organism.

Mutation can be due to a mistake that takes place during copying the DNA during cell division.

Mutagens can increase the chance of mutation, examples of mutagens are ionising radiations: UV rays, gamma rays, x-rays, and chemicals: tar, mustard gas.

A condition caused by an inherited gene that cannot produce the brown pigment in the skin and hair called melanin.

Albinism

A condition caused by a mistake during egg formation, which produces an egg with 24 chromosomes, upon fertilisation a zygote with 47 chromosomes is produced.

Down’s syndrome

Black & peppered moths.

Peppered moth

Black moth

Can mutation be useful?

Is when nature (conditions in the environment) favours the survival of an organism that is more suited to that environment.

This causes the evolution of an organism with time, so that the better suited (adapted) with better genes survive and the one that is less adapted becomes extinct.

Natural selection

Artificial selection

Is when humans chose which two organisms interbreed to produce an offspring with a desired set of genes.

Widely used by farmers to produce a breed that can produce more milk, or better meat or more wool, bigger eggs …etc

Plants can be artificially selectedby crossing the desired flowers to get new offspring with better traits.

Bacterial resistance