2.4 - variation & evolution

Define: variation

Differences between members of the same species

Gives 2 causes of variation

• Genes

• Environment

How does genes cause variation?

Differences in the genotypes of organisms of the same species due to the presence of different alleles

It creates differences in phenotypes

How does environment cause variation?

Differences in phenotype that are acquired by an organism in its lifespan due to environmental factors

E.g. diet, lifestyle, climate, light exposure

What are the 2 types of variation?

• Continuous

• Discontinuous

Describe continuous variation, and give examples

• When a feature changes gradually over a range of values

• E.g. height and weight / 1-20, 21-40, 41-60

Usually forms a bell shaped curve

Describe discontinuous variation, and give examples

• When a feature has a limited number of possible values

• E.g. eye colour, sex, blood group / blood type O, blood type B…

Only certain answers; not ranged

Genetic variation can be due to…

• Sexual reproduction

• Spontaneous mutations

What are the 2 types of reproduction?

• Sexual

• Asexual

How many parents are involved in sexual and asexual reproduction, and do they require sex cells?

• Sexual - 2 parents, sex cells needed

• Asexual - 1 parent, NO sex cells needed

Are offspring genetically different or identical in sexual and asexual reproduction?

• Sexual - genetically different ; meiosis

• Asexual - genetically identical (clones) ; mitosis

Name 4 advantages of sexual reproduction

• Evolution

• Natural selection

• Adaption to environment

• Survival value

Define: mutation

A random change in the bases of DNA

Mutations can be… (3)

• Beneficial

• Harmful

• Have no effect

What can increase mutation rates?

• Ionising radiation

• Strong chemicals

How does a harmful mutation affect an organism?

1. Ionising radiation etc can mutate a base(s) in the DNA

2. Therefore a triplet code is altered and codes for an incorrect amino acid,

3. which forms a non-functional protein (may result in a severe changes to phenotype)

What is cystic fibrosis?

An INHERITED DISEASE that causes the production of thick mucus that blocks the bronchioles, affecting the lungs

How may someone get cystic fibrosis?

A mutation in a gene and can be inherited as a RECESSIVE allele

State if the following would have cystic fibrosis or not:

• NN

• Nn

• nn

• NN - healthy

• Nn - healthy, but a carrier of the faulty allele

• nn - HAS CYSTIC FIBROSIS

What is a treatment for cystic fibrosis, what does it aim to do, and how?

GENE THERAPY

Aims to fix/replace faulty genes via inhaling a good copy of the gene via INHALER

What are 3 disadvantages of gene therapy?

• Difficulty in targeting appropriate cells

• Healthy genes are not passed on

• Only short term / not a cure

Define: natural selection

A process where organisms are better adapted to an environment, and will survive and reproduce

Define: evolution

A process of gradual change that takes place over many generations

What are the 6 steps of natural selection?

(My Very Silly Rat Played Today)

1. Mutation

2. Variation

3. Survive (those with advantageous genes)

4. Reproduce

5. Pass on advantageous genes to next generations

6. “This is natural selection”

What are 3 possible reasons for a species going extinct?

• Organisms are not adapted to their environment

• Organisms have not adapted rapidly enough to changing environmental conditions

• Outcompeted by a better adapted species

Give 3 examples of modern day evolution

1. Antibiotic-resistant bacteria

2. Pesticide resistance

3. Warfarin-resistant rats