Variation & Evolution (WJEC GCSE Science (Double Award): Biology): Flashcards
Exam code: 3430
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Define variation.
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Define variation.
The differences between individuals of the same species.
What are the two main causes of phenotypic variation?
Genetic causes, controlled entirely by genes
Environmental causes, resulting from the conditions the organism lives in
Many features are caused by a combination of both.
Give three examples of genetic variation in humans.
Any three of:
Blood group
Eye colour
Sex
Ability to roll the tongue
Whether ear lobes are free or fixed
Give three examples of environmental variation.
Any three of:
Scarring from an accident
Weight gain from diet and lifestyle
The language and accent a person speaks with
A plant growing taller in the shade to reach light
Explain how height can be caused by both genes and the environment.
Tall parents pass on genes giving their child the genetic potential to be tall.
However, if the child's diet is poor they will not grow well, so the environment also affects the final height.
＿＿＿＿＿＿＿＿ is the term for differences between individuals of the same species.
Variation is the term for differences between individuals of the same species.
True or False?
All variation is caused by genes.
False.
Some variation is caused by the environment, and much of it results from a combination of genes and environment.
Define polymorphic variation.
Variation in which a species shows several distinct forms, such as the different shell patterns in Capaea snails.
Describe how to investigate variation in snail shell patterns across two habitats.
Take a representative sample of 50 snails from each habitat, using quadrats to select them randomly.
Photograph the snails in place rather than removing them.
Categorise each snail into one of the four shell variants and record the results in a tally chart.
Present the results as a bar chart for each habitat.
Name the four shell variants recorded in the snail variation practical.
Pink/brown plain
Yellow plain
Pink/brown striped
Yellow striped
Why are the snails photographed rather than collected?
It is an ethical consideration. Snails are living animals, so the method should avoid removing or harming them.
Suggest why more yellow snails might be found in grassland than in woodland.
Yellow shells give better camouflage against pale grass, so those snails are less likely to be eaten by predators and survive in greater numbers there.
Give two questions you should ask when evaluating this investigation.
Was the sample size big enough and were the snails collected randomly?
Were camouflaged snails missed, biasing the results?
A ＿＿＿＿＿＿＿＿ chart is an efficient way to record the frequency of each snail type.
A tally chart is an efficient way to record the frequency of each snail type.
True or False?
A larger sample size makes the results of a variation study more valid.
True.
A bigger sample is more representative of the population, so conclusions drawn from it are more reliable.
Define continuous variation. (Higher Tier Only)
Variation in which there are many small degrees of difference between individuals, usually measurable on a scale.
Define discontinuous variation. (Higher Tier Only)
Variation in which there are distinct, separate categories with no in-between values.
Give three examples of continuous variation. (Higher Tier Only)
Height
Mass
Finger length
Give three examples of discontinuous variation. (Higher Tier Only)
Blood group, A, B, AB or O
Sex
Ability to roll the tongue
What shape of graph does continuous variation produce? (Higher Tier Only)
A smooth bell-shaped curve, because there are many small degrees of difference.
What shape of graph does discontinuous variation produce? (Higher Tier Only)
A step-like shape, because the data fall into discrete groups.
What usually causes discontinuous variation? (Higher Tier Only)
Genetic variation alone. The environment has little or no effect.
What usually causes continuous variation? (Higher Tier Only)
A combination of genetic and environmental causes.
Height is an example of ＿＿＿＿＿＿＿＿ variation. (Higher Tier Only)
Height is an example of continuous variation.
Blood group is an example of ＿＿＿＿＿＿＿＿ variation. (Higher Tier Only)
Blood group is an example of discontinuous variation.
True or False?
Continuous variation gives a smooth bell-shaped curve when plotted. (Higher Tier Only)
True.
Most individuals fall near the middle of the range, with fewer at each extreme.
True or False?
There are in-between categories for discontinuous variation. (Higher Tier Only)
False.
Discontinuous variation has distinct categories with no in-betweens, e.g. you are either blood group A, B, AB or O.
How can you tell from a graph whether variation is continuous or discontinuous? (Higher Tier Only)
A smooth bell curve indicates continuous variation
A step-like bar chart with separate groups indicates discontinuous variation
Define sexual reproduction.
The fusion of the nuclei of two gametes to form a zygote, producing offspring that are genetically different from each other and from the parents.
Define asexual reproduction.
A process involving only one parent that produces offspring genetically identical to the parent and to each other.
Define clone.
An offspring that is genetically identical to its single parent, produced by asexual reproduction.
Define fertilisation.
The fusion of gamete nuclei, producing a new combination of chromosomes in the zygote.
Name the gametes of animals and of flowering plants.
Animals: sperm cells and egg cells
Flowering plants: pollen cells and egg cells
Explain why sexual reproduction gives rise to variation.
Each gamete comes from a different parent and carries one set of chromosomes.
Fertilisation therefore produces a new combination of chromosomes in the zygote.
Which type of cell division produces gametes, and which is used in asexual reproduction?
Meiosis produces gametes for sexual reproduction
Mitosis alone is used in asexual reproduction
Why does asexual reproduction produce no variation?
There is no fusion of gametes and no mixing of genetic information, so all offspring are genetically identical to the single parent.
The fusion of the nuclei of two gametes forms a ＿＿＿＿＿＿＿＿.
The fusion of the nuclei of two gametes forms a zygote.
Genetically identical offspring produced from a single parent are called ＿＿＿＿＿＿＿＿.
Genetically identical offspring produced from a single parent are called clones.
True or False?
Asexual reproduction requires two parents.
False.
Asexual reproduction requires only one parent and involves no gametes or fertilisation.
True or False?
A gamete contains one set of chromosomes rather than two.
True.
Gametes are formed by meiosis, which halves the chromosome number so fertilisation restores the full set.
Give one advantage of sexual reproduction over asexual reproduction.
It produces variation in the offspring, which means a population is better able to adapt to a changing environment.
Compare the offspring produced by sexual and asexual reproduction.
Sexual: offspring are genetically different from each other and from the parents
Asexual: offspring are genetically identical clones of the single parent
Define mutation.
A random change in an existing gene, which can result in the creation of a new allele.
What effect do most mutations have?
No effect on the phenotype. The protein produced by the mutated gene usually works just as well as before.
Give an example of a beneficial mutation.
A bird develops a change in beak shape that gives it access to a wider range of food.
This increases its chances of surviving and reproducing, so it passes the new allele on.
Give an example of a harmful mutation in humans.
Sickle cell anaemia, which has dramatic effects on the body.
What increases the rate at which mutations occur?
Exposure to ionising radiation, such as gamma rays, X-rays and ultraviolet rays.
The greater the exposure, the higher the chance of mutations in DNA.
Why is exposure to ionising radiation linked to cancer?
It increases the rate of mutation, and mutations in the genes controlling cell division can make cells become cancerous.
Mutations occur at ＿＿＿＿＿＿＿＿, spontaneously and continuously.
Mutations occur at random, spontaneously and continuously.
True or False?
All mutations are harmful.
False.
Most mutations have no effect. A few are harmful, and occasionally one is beneficial and gives a survival advantage.
What is cystic fibrosis and what causes it?
A genetic disorder of cell membranes caused by a mutation.
The body produces large amounts of thick, sticky mucus that blocks the bronchioles and damages the lungs.
How is cystic fibrosis inherited?
As a recessive allele.
A person must be homozygous recessive to have the disorder. Heterozygous people are unaffected carriers.
If both parents are carriers of cystic fibrosis, what is the chance of a child having it?
1 in 4, or 25%.
Define gene therapy.
Inserting working versions of a faulty gene into a person with a genetic disease, in order to treat it.
How is gene therapy delivered to a cystic fibrosis sufferer?
The genes are introduced using an inhaler, so they are breathed into the lung tissue.
Give two reasons why gene therapy is not straightforward.
It is difficult to ensure the correct cells are targeted
It does not alter all the cells of the body, so relief is temporary and treatment must be repeated
A person who carries one recessive cystic fibrosis allele but does not have the disorder is called a ＿＿＿＿＿＿＿＿.
A person who carries one recessive cystic fibrosis allele but does not have the disorder is called a carrier.
True or False?
Gene therapy is a permanent cure for cystic fibrosis.
False.
It is not a cure. It does not alter all the body's cells, so any relief of symptoms is temporary.
What is a family tree used for in the study of inherited conditions?
To show the patterns of inheritance of a disorder through a family, which helps determine the risk to other family members.
Define natural selection.
The process by which individuals with characteristics best suited to their environment are more likely to survive and reproduce, passing those characteristics on.
Define evolution.
The change in the adaptive features of a population over time, as a result of natural selection.
Why is heritable variation essential for evolution?
Only characteristics that can be passed on to offspring can become more common in a population over generations.
Describe the process of natural selection.
Individuals show variation caused by mutations.
More offspring are produced than the environment can support, so there is competition for resources.
Those with the best-adapted characteristics are more likely to survive and reproduce.
They pass their alleles on, so the next generation has more individuals with those characteristics.
Who independently proposed the theory of natural selection?
Charles Darwin and Alfred Russel Wallace.
They published papers together in 1858.
What did Darwin observe on his voyage that led to his theory?
That there was variation within the same species, and that individuals with characteristics most suited to their environment were more likely to survive, reproduce and pass those characteristics on.
What is Wallace best known for?
His work on the warning colouration of species such as butterflies, showing it evolved by natural selection to deter predators, and for developing the theory of speciation.
How can natural selection lead to extinction?
If natural selection acts too slowly for a population to adapt to new environmental conditions, the organisms are not well enough adapted and the species may die out.
Explain how white-shelled snails could come to dominate a pale habitat.
A chance mutation produces a white shell in a few snails.
They are better camouflaged, so they are less likely to be eaten and survive longer.
They therefore get more chances to reproduce and pass the allele on, until most snails have white shells.
Give two limitations of a model used to illustrate camouflage and natural selection.
Any two of:
It is a simplification, considering only one trait when many affect survival
The conditions are fixed, unlike real fluctuating environments
It runs over a short time, giving an unrealistic impression of the speed of evolution
It ignores interactions such as competition, predation and disease
Natural selection is sometimes described as survival of the ＿＿＿＿＿＿＿＿.
Natural selection is sometimes described as survival of the fittest.
Darwin published his book On the Origin of ＿＿＿＿＿＿＿＿ in 1859.
Darwin published his book On the Origin of Species in 1859.
True or False?
Organisms deliberately change themselves to suit their environment.
False.
Variation arises from random mutation. The environment then selects which individuals survive and reproduce.
True or False?
If the environment does not change, selection favours individuals with the same characteristics as their parents.
True.
Evolution is driven by a change in the environment or the appearance of a new allele.
Why does competition arise within a population?
Organisms produce more offspring than the environment can support, so individuals must compete for food and other resources.
Give three examples that show evolution is ongoing today.
Antibiotic resistance in bacteria
Pesticide resistance in insects
Warfarin resistance in rats
Explain how a population of bacteria becomes resistant to an antibiotic.
Random mutations give a few bacteria resistance.
When the antibiotic is used, the resistant bacteria survive while the others die.
They then reproduce with reduced competition, so the resistant population increases.
Why has antibiotic resistance become such a problem?
Antibiotics have been overused since their introduction, which repeatedly selects for resistant strains across many bacterial species.
What is MRSA?
Methicillin-resistant *Staphylococcus aureus*, a strain that has evolved resistance to the powerful antibiotic methicillin.
It infects wounds and is difficult to treat.
What is warfarin, and how have rats become resistant to it?
Warfarin is the active ingredient in rat poison.
Random mutations produced alleles giving some rats resistance. Those rats survive and reproduce, so the resistance allele becomes more common.
Explain how insects become resistant to a pesticide.
Random mutations give some insects natural resistance.
These individuals have a selective advantage, so they survive spraying and pass the allele on.
Over time the resistance allele becomes more common in the population.
Define selective advantage.
A characteristic that makes an individual more likely to survive and reproduce than others in its population.
Why do bacteria evolve resistance so quickly?
They reproduce very rapidly and acquire random mutations, so advantageous alleles spread through the population in a short time.
＿＿＿＿＿＿＿＿ is the active ingredient in rat poison to which some rats have become resistant.
Warfarin is the active ingredient in rat poison to which some rats have become resistant.
Resistance arises in the first place because of ＿＿＿＿＿＿＿＿ mutations in DNA.
Resistance arises in the first place because of random mutations in DNA.
True or False?
Bacteria develop resistance because they are exposed to antibiotics.
False.
Resistance arises by random mutation whether or not antibiotics are present. The antibiotic then selects the already-resistant bacteria.
True or False?
Antibiotics are effective against viruses as well as bacteria.
False.
Antibiotics target structures and processes specific to bacterial cells, so they have no effect on viruses.
What must be done if a resistant strain is causing a serious infection?
A different antibiotic must be used, one to which the strain is not resistant.
Why do these examples all follow the same pattern?
Each begins with random variation from mutation, followed by a selection pressure that allows only some individuals to survive and pass on their alleles. That is natural selection.
Define genome.
The entire set of genetic material of an organism.
What was the Human Genome Project?
An international, collaborative research effort to determine the DNA sequence of the entire human genome and record every human gene. It was completed in 2003.
State three medical benefits of understanding the human genome.
Prediction and prevention of diseases
Testing and treatment for inherited disorders
Development of new and improved medicines
How can knowledge of the genome help prevent diseases such as cancer and heart disease?
Knowing which genes predispose people to these diseases allows doctors to give specific lifestyle and diet advice to help patients avoid or delay their onset.
How has the Human Genome Project helped with inherited disorders?
It allows faulty alleles to be identified much more quickly.
People can then be tested for them and treatments can be developed.
How can genome knowledge improve medicines?
Drugs can be tailored to a person's genetic variations, making them more effective with fewer side effects.
Doctors can also better predict how well a treatment will work for an individual.
Give one psychological drawback of genome knowledge.
Being told you have a high chance of developing a disease may cause anxiety and stress, possibly unnecessarily, since you may never develop it.
How could people with a known faulty allele be discriminated against?
Employers may be unwilling to hire them in case they become ill, and insurers may charge them much more for life insurance.
Give one reproductive concern raised by genome knowledge.
People with a genetic disorder, or who carry a faulty allele, could be pressured into not having children.
The entire set of genetic material of an organism is called its ＿＿＿＿＿＿＿＿.
The entire set of genetic material of an organism is called its genome.
The Human Genome Project was completed in the year ＿＿＿＿＿＿＿＿.
The Human Genome Project was completed in the year 2003.
True or False?
Diseases such as cancer are caused by genes alone.
False.
They are partially caused by genes, but lifestyle factors also play a major part.
True or False?
Knowing a person's genome allows doctors to predict how well a drug will work for them.
True.
Genetic variations affect how people react to diseases and treatments, so predictions can be made and drugs tailored accordingly.
Why was the Human Genome Project described as a collaborative effort?
It was an international project. Scientists from many countries worked together to sequence the whole genome.
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