6.2 Variation (B14)

What is variation?

Differences in characteristics of individuals in a population

Two causes of variation within a species

• Genetics

• Environment

• A mix of genetics and environment

What is genetic Varey

• Variations in the genotype of organisms of the same species due to the presence of different alleles

• Create differences in phenotypes

What creates genetic variation in a species?

• ]Spontaneous mutations

• Sexual reproduction

What is a mutation?

Change to the base sequences in DNA which results in genetic variance ,they occur continuously

Explain how a gene mutation may affect an organism phenotype (three marks)

• Neutral mutation does not change the sequence of amino acids, protein structure and function same no effect on phenotype

• Mutation make towards a minor change in an organism phenotype e.g. change in eye colour

• Mutation may completely change the sequence of amino acids. This may result in a non-functional protein . severe changes to phenotype.

What is the consequence of a new phenotype caused by mutation being suited to an environmental change?

There will be a rapid change in the species

What is evolution?

• A gradual change in the inherited traits within a population overtime

• A cause due to natural selection which may be resulting in the formation of a new species

Outline the theory of natural selection

All species of living things have evolved from simple life forms that first developed more than 3 billion years ago

• Genetic variation exist due to spontaneous mutations

• Selection pressures, e.g. competition and disease exist

• Random mutation gives an organism a selective advantage

• Organism is better adapted to the environment and survives

• Organism reproduce is passing on its beneficial alleles

• Frequency of advantageous alleles increase

How do two populations become different species?

When their phenotypes become different to the extent that they can no longer into breed to produce fertile offspring

What is selective breeding?

The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes

Outline the main steps involved in selective breeding

• Identify a desired characteristic, e.g. disease resistance

• Select parent organisms that show the desired traits and breed them together

• Select offspring with the desired traits and breed them together

• Process repeated into all offsprings have the desired traits

Give examples of characteristics selected for in selective breeding

• Disease resistance in crops

• Higher milk or meat production in animals

• Gentle nature in domestic dogs

• Large flowers

What is the main advantage of selective breeding?

• Create organisms with desirable features such as:

• Crops produce a higher yield of grain

• Plants produce larger fruit

• Cows produce a great supply of milk

• Domesticated animals

Other than in agriculture where else is selective breeding useful

• In medical research

• In sports such as horse racing

Outline the 4 disadvantages of selective breeding

• Reduction in the gene pool, which becomes especially harmful if sudden environmental changes occur

• In breeding results in genetic disorders

• Development of the other physical problems, e.g. respiratory problems in bulldogs

• Potential to unknowingly select harmful recessive alleles

What is genetic engineering

• The modification of the genome of an organism by the insertion of a desired gene from another organism - jeans from chromosomes of humans and other organisms can be cut out and transferred to cells of other organisms

• Enable the formation of an organism with beneficial characteristics

Given an example of uses for genetically modified plants

• Disease resistance

• Produce larger fruits

What is the use for genetically modified bacteria cells?

To produce human insulin to treat diabetes mellitus

Describe three benefits of genetic engineering

• Increased crop yards for growing population, e.g. herbicide resistant and disease resistance

• Useful in medicine, e.g. insulin producing bacteria, antithrombin and goat milk, possibility to overcome some inherited disorders

• GM crops produce scarce resources, e.g. GM golden rice produces beta carotene a source of vitamin A

Describe four risks of genetic engineering

• Long-term effects of consumption of GM crops is unknown

• Negative environmental impacts, e.g. reduction in biodiversity, impact on a food chain, contamination of non-GM crops forming super weeds

• Late onset health problems in GM animals

• GM seeds are expensive and low income development countries may be unable to afford them or maybe dependent on businesses that sell them

How is genetic engineering used to protect crops against insects?

• The gene for toxin production in BT can be isolated and inserted into DNA for crops

• BT crops not secret the toxin which kills any insect larvae that feed on it