Variation & Evolution (AQA GCSE Combined Science: Trilogy: Biology): Flashcards
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Variation
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Variation
The differences in characteristics between individuals of the same species.
What are the three causes of variation?
Genetic causes (the genes inherited)
Environmental causes (the conditions they develop in)
A combination of genes and the environment.
Give an example of genetic variation and of environmental variation in humans.
Genetic: blood group or eye colour.
Environmental: a scar from an accident, or the language and accent a person speaks.
Where do all genetic variants arise from?
From mutations — random changes to genes that occur continuously.
What effect do most mutations have on the phenotype?
Most have no effect on the phenotype.
Some influence it, and very few determine it.
Mutations occur , but only rarely lead to a new phenotype.
Mutations occur continuously, but only rarely lead to a new phenotype.
How can a mutation lead to a relatively rapid change in a species?
If the new phenotype is suited to an environmental change, it gives a survival advantage, so it is passed on and spreads quickly through the species.
Evolution
A change in the inherited characteristics of a population over time, through the process of natural selection.
What does the theory of evolution by natural selection state?
That all species of living things have evolved from simple life forms that first developed more than three billion years ago.
How does evolution occur through natural selection?
Individuals with phenotypes best suited to their environment are more likely to survive and reproduce, passing on the alleles for those features to their offspring.
Speciation
The formation of a new species, which occurs when two populations become so different in phenotype that they can no longer interbreed to produce fertile offspring.
Two populations have become separate species when they can no longer interbreed to produce offspring.
Two populations have become separate species when they can no longer interbreed to produce fertile offspring.
True or False?
Natural selection is the mechanism by which evolution takes place.
True.
Evolution is the change in a species over time, while natural selection is the process by which that change happens.
Selective breeding (artificial selection)
The process by which humans breed plants and animals for particular, desired genetic characteristics.
Describe the steps of selective breeding.
Choose parents with the desired characteristic and breed them together.
Select the offspring with the desired characteristic and breed them together.
Repeat the process over many generations.
Why must selective breeding be repeated over many generations?
So that eventually all offspring reliably show the desired characteristic — producing a new breed.
Give two examples of characteristics chosen by selective breeding.
For example:
Disease resistance in food crops
Cows that produce more meat or milk
Domestic dogs with a gentle nature
What is the impact of selective breeding on humans?
It has increased the yield and quality of food from crops (e.g. rice, fruit) and animals (e.g. meat, eggs, milk), helping the human population to grow.
Inbreeding
Breeding of closely related individuals, which reduces the gene pool (the number of different alleles in a population).
What problems can inbreeding from selective breeding cause?
A reduced gene pool increases the chance of:
inheriting harmful genetic defects
being vulnerable to new diseases.
Selective breeding can lead to , which reduces the number of alleles in a population.
Selective breeding can lead to inbreeding, which reduces the number of alleles in a population.
Genetic engineering
A process that modifies the genome of an organism by introducing a gene from another organism to give a desired characteristic.
Give an example of a genetically engineered plant crop.
For example, crops engineered to be resistant to disease or herbicides, to produce bigger, better fruit, or 'golden rice', which produces beta-carotene (used to make vitamin A).
Why have bacterial cells been genetically engineered?
To produce useful substances, such as human insulin to treat diabetes.
GM crop
A crop whose genes have been modified, e.g. to be resistant to insect attack or herbicides; GM crops generally show increased yields.
Give one benefit and one concern about GM crops.
Benefit: increased yield, resistance to insects or herbicides, or added nutrients.
Concern: effects on populations of wildflowers and insects, or unknown effects on human health.
GM crops that are resistant to insect pests generally show increased .
GM crops that are resistant to insect pests generally show increased yields.
How might genetic engineering be used to treat inherited disorders?
By inserting working versions of faulty genes into people with the disorder — a technique called gene therapy.
Describe the main steps in the process of genetic engineering. (Higher Tier Only)
Enzymes are used to isolate (cut out) the required gene.
The gene is inserted into a vector (usually a bacterial plasmid or a virus).
The vector inserts the gene into the required cells.
Genes are transferred at an early stage of development so the organism develops with the desired characteristics.
In genetic engineering, the isolated gene is inserted into a , usually a bacterial plasmid or a virus. (Higher Tier Only)
In genetic engineering, the isolated gene is inserted into a vector, usually a bacterial plasmid or a virus.
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