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B14 Variation and evolution

B14.1 Variation

Question	Answer
Define variation.	the differences in the characteristics of individuals in a population
What causes variation?	• genes • environment • a combination of genes and environment
Why do siblings share characteristics?	as they inherit their genes from the same parents, their genes are drawn from the same pool meaning siblings will share some but not all characteristics
Why are siblings not identical?	genes are mixed in the production of gametes to produce a unique combination of genes
Name some characteristics that result from genes.	eye colour, nose shape, dimples, gender
What is meant by environment when talking about variation?	the conditions in which organisms grow and live
Name some characteristics due entirely to environment in people.	a scar, hair length, a tattoo
What might cause genetically identical plants to be different?	different amounts of • mineral ions • water • carbon dioxide • light • heat
Is skin colour due to genes or environment?	both - the original skin colour is inherited from parents but it will darken in a sunny environment
Name two human characteristics beside skin colour that are determined by both genes and environment.	height and weight
How is height determined by both genes and environment?	genes determine the maximum potential height an organism can reach, and environmental factors like nutrition, determine how much of that potential is realised
What are genetically identical humans called?	identical twins
Why do scientists study identical twins?	with identical genes, identical twins can help to understand the impact of environment on characteristics
Is it possible to separate identical twins to study how different environmental factors affect their characteritics?	no, this would be unethical
Are there cases of identical twins that have grown up in separate environments?	yes, there are cases where identical twins have been adopted and raised by different families
What does the study of identical twins raised by different families show?	some characteritics are due mainly to genes and some are mainly due to environment
What does the term phenotype mean?	phenotype refers to the observable physical characteristics of an organism
What determines phenotype?	genes, environment, or a combination of both

B14 Variation and evolution

B14.2 Evolution by natural selection

Question	Answer
How have have different species come to exist?	all species of living organisms have evolved from simple life forms that first developed over 3 billion years ago through natural selection
What is this called?	the theory of evolution
What is a scientific theory?	a scientific theory • is a collection of the scientific knowledge on an aspect of the natural world • includes and explains facts related to an aspect of the natural world • includes laws derived from empiracal data • has been repeatedly tested and verified in accordance with the scientific method • has withstood rigorous scrutiny
What is a scientific theory not?	• it is not just an idea • it is not a guess • it is not unproven • it cannot be dismissed as 'just a theory'
What is natural selection?	• animals and plants are in competition with their own species • those that gain an advantage will survive long enough to breed • they will pass their advantage on to their offspring • those that do not have the advantage will not survive to breed • the characteristic that confers an advantage will become more common, even dominate • nature has "chosen" the individuals that will breed
Describe an example of natural selection in action.	• foxes catch rabbits to eat • the fastest rabbits are the most likely to escape being caught • the fastest rabbits are thus most likely to survive and breed • they will pass on the genes which give them their speed • the slowest rabbits are the most likely to be caught and eaten • the slowest rabbits are unlikely to survive and breed • they will not pass on the genes which make them slow • the average speed of the rabbit population will increase
Why do the individual organisms in a species show a wide range of variation?	• partly due to inheriting a mixture of different genes from their parents • partly due to mutations
How do new variants happen?	by mutation
What is mutation?	a change in the DNA code creating a new version of a gene
When can mutations take place?	everytime a cell divides
What is the effect of a mutation?	it may • have no impact • be harmful, sometimes so harmful the organism does not survive • it may introduce a new variant into the genes of a species
What is the most likely impact of a mutation?	either no impact or harmful
What is the least likely outcome of a mutation?	it provides an advantage for survival
What does the theory of evolution state?	all species of living things have evolved by natural selection from simple life forms that first developed more than 3 billion years ago
What does natural selection do?	it produces changes in the inherited characteristics of a population over time that results in organisms that are well suited to their environment
Summarise the process of evolution natural selection.	• individuals with the characteristics most suited to the environment survive to breed • the genes that enabled the breeding individuals to survive are passed on to the next generation • genes are shuffled to produce new combinations in meiosis when gametes are produced • new variants of genes arise from mutations from time to time • new variants of genes sometimes produce advantages for survival and are pased on when breeding • the process repeats itself • over many generations species change as new and different genes dominate • sometimes new species are formed
How quick is change by natural selection?	it varies - generally it takes a long time (thousands of years) but if a particularly advantageus characteristic arises, it can be relatively quick
If people descended from monkeys, why do we not see monkeys evolving into humans today?	• humans did not evolve from monkeys • humans and monkeys share a common ancestor around 25 million years ago • humans are apes • apes share a common ancestor around 6 million years ago • evolution is not linear • evolution is a branching process that gives rise to two or more species
Do humans share DNA with any other living organisms?	• humans share 99.9% of their DNA with other humans • chimpanzees and humans share 98% of their DNA • rhesus monkeys and humans share 93% of their DNA • cats and humans share 90% of their DNA • mice and humans share 85% of their DNA • cows and humans share 80% of their DNA • chickens and humans share 60% of their DNA • bananas and humans share 50% of their DNA
Describe how natural selection protected the oysters of Malpeque Bay in Canada.	• in 1915, fisherman noticed some diseased oysters • by 1922, the disease had wiped out nearly all the oysters • a few oysters were resistant to the disease - they survived to breed • by 1940, the oyster beds had filled up again • as a result of natural selection, the oysters of Malpeque Bay are resistant to the disease
How long does it take for a species to evolve?	it has taken millions of years for most of the species on earth to evolve
What has happened to most species that have evolved?	most species are extinct - only very few have continued to exist to this day
When have new species been formed?	when two populations of a species can no longer interbreed to produce fertile offspring, two new species have formed

B14 Variation and evolution

B14.3 Selective breeding

Question	Answer
What is the process called when humans try to speed up evolution?	selective breeding
What is the goal of selective breeding?	to breed plants and animals for desired characteritics
List some examples of characteristics achieved through selective breeding.	• disease resistance in plants • animals that produce more meat • domestic dogs with a gentle nature • highly scented flowers • cows that produce more milk • larger seeds in cereals • large, brightly coloured flowers
How does selective breeding work?	• individuals with desired characteristics are selected from a mixed population • these individuals are bred to produce offspring • offspring are selected with desired characteristics • the process is repeated until the required result • it works for plants and animals
How have diary cows changed as a result of selective breeding?	the aggressive wild ancestor of cows that only produce enough milk for one calf have become placid, friendly cows that produce 15 to 25 litres per day for 10 months
How has wheat changed as a result of selective breeding?	the thin, needle-like grains of wild wheat have increased hundreds of times in size with many more grains on each stalk
What is the major problem with selective breeding?	it reduces the number of alleles in in the population
Why are the numbers of alleles reduced?	because only the individuals with the chosen alleles are allowed to breed
What is the consequence of reducing the number of alleles in a population?	it reduces the variation in the population
What is the impact of reducing variation in a population?	when conditions are stable there is no problem but when conditions change, it may be that none of the population can cope with the change
Name a problem which may be a threat to a population with limited variation?	a new disease - if it can infect one member of the population, it may infect all, and in the worst case wipe them out
Why is the risk to the modern banana industry?	bananas are genetically very, very similar so if a new disease manages to kill one banana plant, it may very well wipe most or all out, destroying the industry quickly
Aside from limited variation, what is the other major problem with selective breeding?	selective breeding offers means breeding closely related individuals making the offspring prone to specific diseases or increasing the chance of inherited defects
What is inbreeding?	breeding closely relatied individuals to select for desirable characteristics
List examples of prominent inherited defects due to selective breeding.	• King Charles spaniels have brains that are too large for their skulls • pugs in the UK struggle to breathe • boxer dogs are at high risk of epilepsy • persian cats have watering eyes due to their very flat skulls • some cows have problems giving birth because their calves are so big

B14 Variation and evolution

B14.4 Genetic engineering

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B14 Variation and evolution

B14.5 Cloning (single science only)

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B14 Variation and evolution

B14.6 Adult cell cloning (single science only)

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B14 Variation and evolution

B14.7 Ethics of genetic technologies

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