Variation And Natural Selection

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Variation

Variation refers to differences between individuals of the same species, giving rise to different phenotypes.
Continuous variation shows a range of phenotypes with no distinct categories (e.g., height, body mass).
Continuous variation produces a smooth bell-shaped curve when plotted as a frequency histogram.
Discontinuous variation results in a limited number of distinct phenotypes (e.g., blood group, pea seed shape).
Discontinuous variation produces a step-shaped bar graph.
Mutation is a genetic change involving alterations to DNA, leading to new alleles and phenotypic variation.

Distribution of height showing continuous variation

Natural Selection

Natural selection is the process where better adapted individuals survive and reproduce more successfully.
Individuals in a species show variation due to genetic differences.
Overproduction of offspring leads to competition for resources and a struggle for survival.
Individuals with advantageous alleles are more likely to survive and reproduce.
Advantageous alleles are passed on to offspring, increasing in frequency over generations.
Example: Peppered moths – environmental change made the dark allele advantageous, leading to increased frequency.

Natural selection in peppered moths

Natural Selection: Antibiotic Resistance (Extended)

Variation in bacteria includes some with resistance alleles to an antibiotic.
Exposure to antibiotic kills non-resistant bacteria; resistant ones survive and reproduce.
The resistance allele is passed on, becoming more common in the population.
Over time, the entire population becomes an antibiotic-resistant strain.
Key steps: variation → competition → survival of fittest → inheritance of advantageous alleles.

Natural selection in bacteria: antibiotic resistance

Artificial Selection (Selective Breeding)

Selective breeding is the process where humans choose individuals with desirable characteristics to breed.
Selected individuals are crossed together, and offspring with the desired traits are chosen.
This process is repeated over many generations to enhance the traits.
Examples: dog breeds with calm temperaments, crop varieties with high yield or pest resistance.
Selective breeding has produced a wide range of domestic varieties from wild ancestors.

Selective breeding of dog breeds from wolves

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Practice questions

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1.Which of the following is an example of discontinuous variation?
Easy
- AHeight in humans
- BBody mass in dogs
- CBlood group in humans
- DLeaf length in plants
2.Continuous variation produces a limited number of distinct phenotypes.
Easy
True or false?
3.Define variation.
Easy
4.Complete the sentence about natural selection:
Easy
Individuals that are better ____ to their environment have a higher chance of survival and more chances to reproduce.
5.Place the following steps of natural selection in the correct order:
Medium
- Advantageous alleles become more common in the population
- Individuals in a species show variation
- Better adapted individuals survive and reproduce
- Struggle for survival due to competition
6.What is the source of new alleles in a population?
Easy
7.Match each type of variation with its correct description:
Easy
- Continuous variation
- Discontinuous variation
- Shows a range of phenotypes
- Results in a limited number of phenotypes
8.In a population of bacteria, 5% initially carry a resistance allele. After exposure to an antibiotic, 80% of the surviving bacteria carry the resistance allele. If the survival rate of non-resistant bacteria is 0.1%, what is the survival rate of resistant bacteria? (Assume the population was large and the antibiotic killed all non-resistant bacteria that did not survive.)
Hard
- A10
- B7
- C8
- D9

More questions

9.Explain how antibiotic resistance can develop in a bacterial population.
Medium
10.Which of the following is a step in artificial selection?
Easy
- AIndividuals with desirable characteristics are selected by humans
- BIndividuals with undesirable characteristics are removed by predators
- CIndividuals compete for resources in their environment
- DIndividuals with advantageous alleles survive due to environmental change
11.Selective breeding is also known as artificial selection.
Easy
True or false?
12.Complete the sentence about selective breeding:
Easy
Selective breeding over many generations eventually results in crop and domestic animal ____ which all show characteristics chosen by humans.
13.Which of the following is an example of artificial selection?
Medium
- APeppered moths becoming darker after industrial pollution
- BBacteria developing resistance to antibiotics
- CDog breeds being developed from wolves
- DGiraffes evolving long necks to reach high leaves
14.Match each type of variation with its correct example.
Easy
- Continuous variation
- Discontinuous variation
- Body length
- Blood group
- Height
- Pea seed shape
15.Place the following steps of natural selection in the correct order.
Medium
- Individuals with advantageous alleles survive and reproduce
- Variation exists in a population due to differences in genes
- Advantageous alleles become more common over generations
- Reproduction leads to many offspring, causing competition for resources
16.Which of the following are examples of discontinuous variation? (Select all that apply.)
Medium
- ABody mass
- BBlood group
- CPea seed colour
- DHeight
- EHuman eye colour
17.Mutation results in the formation of new alleles.
Easy
True or false?
18.In a population of bacteria, some individuals have a mutation that makes them resistant to an antibiotic. When the antibiotic is applied, what is the most likely outcome?
Medium
- AAll bacteria die immediately
- BResistant bacteria survive and reproduce, passing on the resistance allele
- CNon-resistant bacteria mutate to become resistant
- DThe antibiotic kills all bacteria, including resistant ones
19.Which of the following is NOT a step in artificial selection?
Medium
- AHumans select individuals with desirable characteristics
- BIndividuals with desirable characteristics are bred together
- COffspring with undesirable characteristics are removed from the population by natural predators
- DThe process is repeated over many generations
20.Which of the following are true about natural selection? (Select all that apply.)
Medium
- AIt results in the evolution of populations over time
- BIt is driven by environmental factors
- CIt always leads to antibiotic resistance
- DIt requires variation in a population
21.Match each term with its correct description.
Medium
- Continuous variation
- Discontinuous variation
- Mutation
- Natural selection
- A change in DNA that creates new alleles
- A process where better-adapted individuals survive and reproduce
- Variation that shows a range of phenotypes
- Variation that results in a limited number of phenotypes
22.Place the following steps of selective breeding in the correct order.
Medium
- Choose offspring that show the desirable characteristics and breed them together
- Select individuals with desirable characteristics
- Repeat the process over many generations
- Cross the selected individuals together
23.In a population of wildflowers, flower colour shows continuous variation. Which of the following statements about this population is correct?
Medium
- AFlower colour falls into distinct categories such as red, white, or blue.
- BFlower colour shows a range of phenotypes with no clear boundaries.
- CFlower colour is determined by a single gene with two alleles.
- DFlower colour does not vary within the population.
24.Mutations always result in a change to the phenotype of an organism.
Easy
True or false?
25.Match each type of variation with its correct description.
Easy
- Continuous variation
- Discontinuous variation
- Produces a limited number of distinct phenotypes
- Shows a range of phenotypes with no clear boundaries
26.A farmer selectively breeds cows to increase milk yield. Which of the following is the most likely long-term consequence of this practice?
Medium
- AThe cows will become more genetically diverse.
- BThe cows will become less genetically diverse.
- CThe cows will become less resistant to disease.
- DThe cows will produce milk with higher fat content.
27.Which of the following is the source of new alleles in a population?
Easy
- ANatural selection
- BMutation
- CSelective breeding
- DCompetition
28.Artificial selection always leads to organisms that are better adapted to their natural environment.
Easy
True or false?
29.Which of the following are necessary conditions for natural selection to occur in a population? (Select all that apply.)
Medium
- AVariation among individuals
- BAll individuals are genetically identical
- COverproduction of offspring leading to competition
- DIndividuals with advantageous traits are more likely to survive and reproduce
- EThe environment is constant and unchanging
30.In a laboratory experiment, a student investigates the effect of an antibiotic on two bacterial strains: one resistant (R) and one non-resistant (S). Equal numbers of each strain are mixed and grown on a nutrient agar plate containing the antibiotic. After 24 hours, the plate is examined. Which of the following results would best demonstrate natural selection?
Medium
- AOnly strain R colonies are present
- BBoth strains R and S colonies are present in equal numbers
- COnly strain S colonies are present
- DNo colonies are present
31.Which of the following is a correct definition of variation?
Easy
- ADifferences between individuals of the same species
- BDifferences between individuals of different species
- CSimilarities between individuals of the same species
- DChanges in an individual during its lifetime
32.Place the following steps of natural selection in the correct order from first to last.
Medium
- Well-adapted individuals survive and reproduce
- Advantageous alleles become more common in the population
- Individuals in a species show variation caused by differences in genes
- There is a struggle for survival due to competition
33.Natural selection always results in organisms that are perfectly adapted to their environment.
Easy
True or false?
34.Match each type of variation with its correct characteristic.
Medium
- Continuous variation
- Discontinuous variation
- produces a bell-shaped curve when plotted
- produces a step-shaped bar graph
- results in a limited number of phenotypes
- shows a range of phenotypes
35.Place the following steps of selective breeding in the correct order from first to last.
Medium
- Choose offspring with the desired characteristics and breed them together
- Select individuals with desirable characteristics
- Repeat the process over many generations
- Cross the selected individuals together
36.Which of the following is an example of continuous variation?
Easy
- ABlood group
- BGender
- CHeight
- DSeed shape
37.A farmer selectively breeds cows for increased milk yield. After 20 generations, the average milk yield has increased by 40%. However, the cows are now more susceptible to a common disease. Which statement best explains this observation?
Hard
- ANatural selection has reduced genetic diversity in the herd.
- BSelective breeding has reduced genetic diversity, making the population more vulnerable.
- CThe disease has evolved to become more virulent over time.
- DIncreased milk yield directly causes immune suppression.
38.Which of the following are examples of continuous variation? (Select all that apply.)
Medium
- AHuman height
- BBlood group
- CSeed shape in peas (round or wrinkled)
- DBody mass in mice
- ENumber of petals in a flower species
39.Place the following steps of natural selection in the correct order from first to last:
Medium
- Advantageous alleles become more common in the population over generations
- Individuals in a species show variation due to differences in genes
- Individuals with advantageous characteristics survive and reproduce more
- Reproduction results in many offspring, leading to competition for resources
40.A population of 1000 birds lives on an island. Their beak sizes show continuous variation, with a mean of 10 mm. After a drought, only seeds with hard shells are available. The average beak size in the next generation is 12 mm. Which statement best explains this change?
Hard
- ABirds with larger beaks learned to crack hard seeds and taught their offspring.
- BBirds with larger beaks had a higher survival and reproduction rate because they could crack the hard seeds, passing on the alleles for larger beaks.
- CThe drought caused a mutation that increased beak size in all birds.
- DBirds with smaller beaks migrated to another island.
41.Variation is defined as differences between individuals of the same species.
Easy
True or false?
42.Discontinuous variation shows a range of phenotypes with no clear categories.
Easy
True or false?
43.In natural selection, individuals that are better adapted to their environment have a higher chance of survival and reproduce more, passing on their alleles.
Easy
True or false?
44.Complete the sentence about variation:
Easy
Differences between individuals of the same species are called ____. Variation can be caused by differences in ____.
45.In a population of bacteria, 5% initially carry a resistance allele. After exposure to an antibiotic, 80% of the surviving bacteria carry the resistance allele. If the total population before exposure was 10,000 and 90% died, how many bacteria survive?
Medium
46.Define the term 'selective breeding' (artificial selection).
Easy
47.Complete the sentence about variation.
Easy
Variation can be defined as differences between individuals of the same ____.
48.In a population of 1000 bacteria, 10% have a mutation that confers antibiotic resistance. After exposure to an antibiotic, 80% of the surviving bacteria carry the resistance allele. If 500 bacteria survive, how many resistant bacteria were there initially?
Medium
49.Define the term 'variation' as used in biology.
Easy
50.In a population of 500 insects, 20 have a mutation that makes them resistant to a pesticide. The pesticide is sprayed, killing all non-resistant insects. What percentage of the surviving insects are resistant? Give your answer to one decimal place.
Easy
51.Describe how natural selection can lead to the development of antibiotic resistance in bacteria.
Medium
52.Explain how artificial selection differs from natural selection.
Medium
53.Explain how the development of antibiotic resistance in bacteria is an example of natural selection.
Medium
54.Explain how natural selection can lead to the development of antibiotic resistance in bacteria.
Medium
55.In a population of bacteria, 5% initially carry a resistance allele. After exposure to an antibiotic, 80% of the surviving bacteria carry the resistance allele. If the total population before exposure was 10,000 and 90% died, how many bacteria survive?
Hard
- A1200
- B1000
- C900
- D1100
56.In a population of 1000 bacteria, 10% have a mutation that confers antibiotic resistance. After exposure to an antibiotic, 80% of the surviving bacteria carry the resistance allele. If 500 bacteria survive, how many resistant bacteria were there initially?
Medium
- A90 bacteria
- B100 bacteria
- C110 bacteria
- D120 bacteria
57.In a population of 500 insects, 20 have a mutation that makes them resistant to a pesticide. The pesticide is sprayed, killing all non-resistant insects. What percentage of the surviving insects are resistant? Give your answer to one decimal place.
Easy
- A100 %
- B120 %
- C110 %
- D90 %

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