Topic 10 - Variation and Evolution Flashcards
What is variation?
Variation describes differences in the characteristics of individuals.
What is variation the result of?
Genetics and the environment
What is genetic variation?
All genetic variation is the result of mutations, some of which are then inherited and passed onto the next generation.
What is continuous variation?
Continuous variation results in a range of phenotypes between two extremes e.g. height
What is discontinuous variation?
Discontinuous variation results in a limited number of phenotypes with no intermediates, usually caused by genes alone e.g. tongue rolling
What is a mutation?
Mutations are random and permanent changes to the base sequence of existing genes, creating new alleles.
Do mutations always affect the phenotype?
Most mutations do not affect the phenotype. Mutations that do affect phenotype can have positive or negative effects.
What rate do mutations happen at?
Mutations are rare. The rate of mutations can be increased by ionising radiation and some chemicals.
What happens if the mutation helps an organism to survive?
This organism will be better adapted to environmental changes than the rest of the population, so it is likely to spread throughout the population over a few generations.
What are the features of asexual reproduction?
Cells divide by mitosis, offspring are clones, no gamete fusion and only one parent.
What are the features of sexual reproduction?
Cells divide by meiosis, offspring are non-identical, gamete fusion and two parents.
How can disorders be inherited?
If parents have certain (usually recessive) alleles.
What is cystic fibrosis?
Cystic fibrosis is a disorder of cell membranes. It causes thick, sticky mucus to build-up in the lungs and digestive system.
What kind of allele causes CF?
Recessive
What is gene therapy?
Gene therapy involves replacing the diseased allele in the cells of a patient with a normal allele of the same gene.
What are the advantages of gene therapy?
This can reduce the symptoms of cystic fibrosis and increase a patient’s life expectancy and quality of life.
What are the disadvantages of gene therapy?
Since the diseased allele is in every cell, it is difficult to replace the gene so it doesn’t always work. It may wear off as healthy cells are replaced by the patient’s cells with the diseased gene.
What can be used to visualise the transmission of inherited disorders from generation to generation?
Family trees
When was the Human Genome Project completed?
2003
What are the benefits of the understanding gained from the HGP?
Improving our understanding of inherited diseases, gene identification, personalised medicine and gene therapy.
Who theorised natural selection?
Charles Darwin
Natural Selection 1
Genetic variation - Different individual animals in a population have different combinations of genes.
Natural Selection 2
Survival of the fittest - Individuals that are best adapted to the environment will have a greater chance of survival.
Natural Selection 3
Successful breeding - Individuals with the best chances of survival are the most likely to breed successfully.
Natural Selection 4
Best characteristics survive - The characteristics responsible for the greater chance of survival are more likely to be passed on to the next generation.
Who else researched natural selection?
Alfred Russel Wallace
What had both Charles Darwin and Alfred Russel Wallace done?
They both spent significant time on islands; the isolation of populations lead to enhanced speciation rates.
What is speciation?
The formation of new species
In which year did they combine their minds?
In 1858, they produced joint writings.
What did Darwin do after they had produced their joint writings?
Darwin accelerated the publication of ‘On The Origin of Species’ to be the first of the two to publish.
When did Darwin develop his theory?
Whilst aboard the HMS Beagle, on an expedition to the Galapagos Islands.
What is an extinction?
When there are no individuals of a species left in the world.
What can cause an extinction?
A change in abiotic (physical) or biotic (relating to organisms) factors can cause an extinction if a species cannot adapt fast enough.
What is resistance?
Resistance can evolve when a small number of individuals survive a certain threat and survive to reproduce, passing their resistance to the threat onto all their offspring.
What is warfarin?
A common ingredient in rat poison
What happens if a rat mutates to be resistant to warfarin?
It will survive when all other rats in the population are killed. The surviving rat will reproduce, creating a population of warfarin-resistant rats.
What are pesticides?
Chemicals often sprayed onto crops to kill insect pests like aphids.
What happens if an aphid mutates to be resistant to pesticides?
It will survive and reproduce to create a new population of aphids resistant to that pesticide.
The pesticide will no longer be effective.
What happens if a pathogen mutates to be resistant to antibiotics?
When a person is treated with antibiotics, the bacteria will survive and go on to reproduce; this is the original ancestor of a new resistant strain. This bacteria will spread, as there will be no treatment for it, people are not immune to it and competition has been reduced.
Why do bacteria evolve particularly quickly?
Bacteria reproduce very rapidly and mutations arise in reproduction, bacteria evolve especially quickly.
When is a new species created?
When 2 populations have diverged so much that they cannot breed fertile offspring.
What is stabilising selection?
A type of natural selection that favours the average phenotype.
What is directional selection?
A type of natural selection that favours an extreme phenotype that takes place after an environment has experienced a change.
Which type of selection is most likely to take place in environments that don’t change?
Stabilising selection
