Variation and mutation

Apprends en jouant

Réponds à ces questions pour gagner de l'énergie, puis pêche et explore. Sans compte.

Pour les enseignants : diapos de leçon, notes de révision prêts à l'emploi pour Variation and mutation (MYP Biology, Year 3) — utilise-les en cours, ou lance le thème en activité de classe interactive que tes apprenants jouent en direct.

Notes de leçon

Big idea: no two individuals are quite the same

Big idea (key concept): Change. Populations are never fixed. New differences keep appearing, and over many generations the features of a species can change.
Related concept: Evidence. We can collect and measure evidence about variation, such as heights, leaf lengths or blood groups, and use it to decide whether genes or the environment cause a difference.
Global context: Identities and relationships. Your features come from the DNA you inherited and from the life you have lived. Understanding variation helps explain why family members look alike but are never identical.
Variation means the differences between individuals. It exists within a species (two dogs of different breeds, two pupils in your class) and between species (a dog and a daisy). In this topic we study variation within one species.
Variation matters because it is the raw material for natural selection. If every individual were identical, a change in the environment could harm them all at once.

Dogs of different breeds, all one species

Continuous and discontinuous variation

Continuous variation means a characteristic can take any value within a range, with no gaps. Examples: height, mass, leaf length, foot length. You measure these, and you can always find a value between two others.
Discontinuous variation means a characteristic falls into separate categories with no in-between values. Examples: ABO blood group (A, B, AB or O), whether a pea seed is round or wrinkled, whether a person has XX or XY sex chromosomes.
For continuous data, collect measurements into groups (for example 150 to 154 cm) and draw a histogram: the bars touch because the scale has no gaps. For discontinuous data draw a bar chart with gaps between the bars, because the categories are separate.
To summarise continuous data use the mean (add the values and divide by how many there are) and the range (largest minus smallest).
Continuous variation is usually affected by many genes and the environment. Discontinuous variation is usually controlled by one or a few genes, with little effect from the environment.

Continuous and discontinuous variation compared

Causes of variation: genes, environment and sexual reproduction

Genetic variation is caused by different alleles, which are different versions of a gene. You inherit your alleles from your parents. Eye colour and blood group are examples.
Environmental variation is caused by conditions during life: a plant grown in the shade is paler and taller than a clone grown in the sun, and a scar is not inherited at all.
Many features depend on both. Your genes set a possible range for height, but diet, health and exercise during growth decide where you end up. Identical twins begin with the same genes, so differences between them are mostly caused by environment.
Height in a large group forms a bell-shaped distribution. Most people are near the mean because many genes each add a small effect, and the environment adds more.
Sexual reproduction produces genetic variation. Each parent makes gametes by meiosis, and each gamete gets a random mix of one chromosome from each of the 23 pairs. That gives about 8 million (2 to the power 23) possible combinations from one person, before any other shuffling. Fertilisation is also random, because any sperm could fertilise any egg.
Asexual reproduction makes offspring that are genetically identical to the parent (clones), so apart from mutations there is no new genetic variation.

Height in a population forms a bell-shaped distribution

Mutations: random changes to DNA

A mutation is a change in the sequence of bases in DNA. A gene is a code of bases read in groups of three, and each group codes for an amino acid. Changing the bases can change the amino acids and so change the protein.
Small mutations change one base (a substitution) or add or remove bases (an insertion or deletion). Larger mutations change the structure of a whole chromosome, for example when a section flips over (an inversion).
Mutations happen at random and by chance. They occur naturally as mistakes when DNA is copied before cells divide. The rate goes up with ionising radiation (X-rays and gamma rays), with ultraviolet light, and with some chemicals, such as those in tobacco smoke.
A mutation in a body cell, such as a skin cell, can harm that cell or its descendants, but it is not passed on to children. Only a mutation in the cells that make gametes can be inherited.
A mutation produces a new allele. This is the only way entirely new alleles arise, so mutation is the original source of all genetic variation.

A normal set of chromosomes and a set with a structural change

Harmful, neutral and beneficial mutations

Most mutations are neutral. The change might be in a part of the DNA that does not code for anything, or the new base group might still code for the same amino acid. The organism looks and works exactly as before.
Some mutations are harmful. If the protein no longer works, the cell or organism can be affected. A mutation that causes cells to divide out of control can lead to cancer. Albinism, where no pigment is made, is another example.
A few mutations are beneficial. A mutation that lets some adults keep digesting lactose (milk sugar) helps in communities that drink milk. A mutation that makes a pest insect resistant to an insecticide helps the insect, though not the farmer.
The environment decides. The sickle cell mutation changes one amino acid in haemoglobin. People with two copies of the allele have sickle cell disease. But people with one copy are better protected against malaria. In regions with malaria the allele stays fairly common. In regions without malaria it has no such benefit.
So a mutation is not good or bad by itself. Whether it helps depends on the protein it changes and the conditions the organism lives in.

A mutation in the haemoglobin gene causes sickle-shaped cells

Think like a scientist: nature or nurture?

Question: does the amount of light a plant gets affect how tall it grows? Use bean seeds from the same pack so that their genes are as similar as possible.
The independent variable is the light level (for example full light, partial shade, dark cupboard). The dependent variable is plant height after two weeks, measured in cm.
Control variables to keep the same: type of seed, volume and timing of watering, compost, pot size and temperature.
To make results reliable, use at least five plants per light level, repeat the investigation and calculate a mean for each level. Look at the range too. A very large range suggests the plants differed for another reason.
Inquiry task 1: plan this investigation and say how you would record and display the results. Inquiry task 2: a student measures one plant per light level and concludes that light controls height. Evaluate the conclusion and suggest two improvements.

Diapos

Step through every slide for this topic — plus flashcards and revision notes — with a free account.

S'INSCRIRE — GRATUIT CONNEXION

Questions d'entraînement

Aperçu gratuit — 8 sur 49 questions. Inscris-toi pour toutes les voir.

1.What does the word variation mean in biology?
Easy
- AThe change from one generation to the next
- BDifferences between individuals of the same species
- CDifferences between living and non-living things
- DThe number of species living in one habitat
2.Which of these shows continuous variation?
Easy
- AThe ABO blood groups of pupils
- BWhether pea seeds are round or wrinkled
- CWhether a person has XX or XY chromosomes
- DThe heights of pupils in a class
3.Which of these shows discontinuous variation?
Easy
- AABO blood group
- BMass of a person
- CLength of a leaf
- DLength of a foot
4.Continuous variation puts individuals into separate categories with no in-between values.
Easy
True or false?
5.Identical twins start life with the same genes.
Easy
True or false?
6.Which of these is caused by the environment rather than by genes?
Easy
- AWhich blood group a person has
- BWhether a person is XX or XY
- CA scar on a knee from a fall
- DThe colour of a pea flower
7.What is a mutation?
Easy
- AA change in the number of cells in the body
- BA disease caused by a virus entering a cell
- CA change in the sequence of bases in DNA
- DA change in the habitat where a species lives
8.Which of these can increase the rate of mutation?
Easy
- AIonising radiation such as X-rays
- BDrinking more water each day
- CEating a diet rich in protein
- DSleeping for longer each night

Plus de questions

9.Mutations happen at random.
Easy
True or false?
10.A mutation that has no effect on the organism is called
Easy
- Aharmful
- Bbeneficial
- Cinherited
- Dneutral
11.Complete the sentence.
Easy
Offspring from sexual reproduction get a mixture of alleles from their two ____.
12.Complete the sentence.
Easy
Blood group is an example of ____ variation.
13.Match each term to its meaning.
Easy
- Variation
- Mutation
- Continuous variation
- Discontinuous variation
- A random change in DNA
- Separate categories with no in-between
- Differences between individuals
- A smooth range of values
14.Put these steps in order to show how a mutation can be passed on to a child.
Easy
- A gamete carries the changed allele
- A mutation happens in a cell that makes gametes
- A gamete fuses with another gamete at fertilisation
- Every cell in the offspring carries the mutation
15.Four bean plants had heights of 12 cm, 15 cm, 18 cm and 15 cm. What is the mean height?
Easy
16.Why are brothers and sisters, who are not identical twins, not exactly alike?
Easy
- AThey always have different parents
- BEach gamete carries a different mix of alleles
- CThey all grow up in separate places
- DMutations occur in every child they have
17.Every mutation is harmful to the organism.
Easy
True or false?
18.Which of these can cause mutations? (select all that apply)
Easy
- AX-rays
- BChemicals in tobacco smoke
- CCold weather
- DMistakes when DNA is copied
- EEating vegetables
19.In a fair test only the independent variable is changed on purpose.
Easy
True or false?
20.Two cuttings from the same plant are genetically identical. One is grown in sunlight and one in shade. The shaded plant is taller and paler. What causes the difference?
Medium
- ADifferent alleles in each plant
- BThe environment, because the genes are the same
- CA mutation in the shaded plant
- DThe shaded plant is a different species
21.Why is human height an example of continuous variation?
Medium
- AOne gene controls it and the environment has no effect
- BPeople are either tall or short with nothing in between
- CIt is caused by mutations in the body cells
- DMany genes and the environment together give a smooth range
22.In sickle cell disease one base in the haemoglobin gene is changed. How does this affect the red blood cell?
Medium
- AOne amino acid changes, so haemoglobin folds into a different shape
- BHaemoglobin is no longer made by the bone marrow cells
- CThe red blood cell gains an extra nucleus to cope
- DThe cell starts to make extra oxygen for the blood
23.Why can a mutation in a gene change the protein that the gene makes?
Medium
- AThe cell membrane then lets different substances in
- BThe nucleus breaks down, so no protein can be made at all
- CThe bases are a code, so a new base can mean a new amino acid
- DMutations make the cell copy its DNA more slowly each time
24.A skin cell is damaged by ultraviolet light and develops a mutation. Will the mutation be passed to the person's children?
Medium
- AYes, because all mutations are passed to children
- BYes, because skin cells make most of the gametes
- CNo, because only mutations in gamete-making cells are inherited
- DNo, because mutations in the skin are always repaired
25.A human gamete gets one chromosome from each of 23 pairs, chosen at random. About how many different combinations of chromosomes can one person make?
Medium
- AAbout 8 million
- B23
- C46
- DExactly 2
26.How do the offspring of asexual reproduction usually compare with the parent?
Medium
- AThey are always completely different
- BThey have half of their genes from each of two parents
- CThey show more variation than sexual offspring
- DThey are genetically identical, apart from any mutations
27.Which of these are sources of genetic variation in sexual reproduction? (select all that apply)
Medium
- AEach gamete gets a random mix of chromosomes
- BAny sperm can fertilise any egg by chance
- CMitosis copies cells exactly
- DMutations in an adult's body cells
- ETwo parents each give a set of alleles
28.Which of these is an example of a beneficial mutation?
Medium
- AA change that makes cells divide without control
- BA change that lets some adults keep digesting milk sugar
- CA change that stops an animal making any pigment
- DA change that has no effect on any protein made
29.People with one copy of the sickle cell allele are better protected against malaria. What does this show about mutations?
Medium
- AAll harmful mutations are really beneficial
- BWhether a mutation helps depends on the environment
- CMutations are always caused by the mosquito
- DA mutation is the same in every environment
30.A person's height is affected by both their genes and their diet.
Medium
True or false?
31.Match each type of mutation effect to the best example.
Medium
- Harmful
- Neutral
- Beneficial
- Cells divide out of control
- A base changes but the same amino acid is still coded
- An insect can survive an insecticide
32.Put the stages of the bean plant investigation in a sensible order.
Medium
- Write a conclusion that refers to the results
- Plan the method and decide which variables to control
- Calculate the mean height for each light level
- Ask a question and make a prediction
- Grow the plants and measure their heights
33.A class survey measured the lengths of five leaves from one bush: 6.1 cm, 7.4 cm, 6.8 cm, 7.0 cm and 7.2 cm. What is the mean length?
Medium
34.For the five leaf lengths 6.1, 7.4, 6.8, 7.0 and 7.2 cm, what is the range?
Medium
- A6.9 cm
- B0.8 cm
- C13.5 cm
- D1.3 cm
35.A student plans to grow bean plants in full light, shade and darkness. What is the independent variable?
Medium
- AThe amount of light the plants receive
- BThe height of each plant after two weeks
- CThe type of seed used in every pot
- DThe volume of water given each day
36.Which of these should be a control variable in the bean plant investigation?
Medium
- AThe amount of light each plant receives
- BThe final height of each plant
- CThe volume of water given to each plant
- DThe conclusion the student expects
37.A class records the blood group of every pupil. Which chart is best for the results?
Medium
- AA histogram with the bars touching
- BA line graph joining each blood group
- CA bar chart, with gaps between the bars
- DA scatter graph of blood group against mass
38.Complete the sentence.
Medium
A mutation that makes no difference to the organism is described as ____.
39.Explain why identical twins can look different as adults.
Medium
40.
In a class survey, the heights of 30 pupils were put into groups.
Height (cm) Number of pupils
150 to 154 3
155 to 159 8
160 to 164 11
165 to 169 6
170 to 174 2
Which description best fits these results?
Hard
- AA bell-shaped spread with most pupils at 160 to 164 cm, typical of continuous variation
- BTwo separate groups with nothing in between, typical of discontinuous variation
- CAn equal number of pupils in every group, so height is not varied
- DMost pupils at 150 to 154 cm, with the number rising steadily afterwards
41.Using the same class survey (150 to 154 cm: 3 pupils, 155 to 159 cm: 8, 160 to 164 cm: 11, 165 to 169 cm: 6, 170 to 174 cm: 2), how many pupils were 160 cm or taller?
Hard
42.A student studies one family. The parents are tall and so are their three children. The student concludes that height is controlled only by genes. What is the best criticism?
Hard
- AHeight is never affected by genes in any way at all
- BChildren are always shorter than their parents
- CThree children are far too many children to measure
- DThe sample is tiny and relatives share an environment
43.The sickle cell allele is harmful, yet it is common in regions where malaria occurs. What is the best explanation?
Hard
- AThe malaria parasite causes the mutation in every child
- BCarriers with one copy are protected from malaria and pass it on
- CThe allele is only ever harmful when it is rare
- DPeople with two copies are the only ones who survive malaria
44.A mutation changes one base in a gene, but the protein it makes is exactly the same as before. What is the most likely reason?
Hard
- AThe mutation was removed from the cell before the protein was made
- BThe new group of three bases codes for the same amino acid
- CMutations never change the sequence of bases
- DThe protein is made in the nucleus where DNA cannot change
45.A beneficial mutation is beneficial in every environment.
Hard
True or false?
46.Which of these would make the bean plant investigation more reliable? (select all that apply)
Hard
- AUse at least five plants at each light level
- BRepeat the whole investigation
- CCalculate a mean height for each light level
- DUse a different seed variety for each light level
- EChange the light level and the watering together
47.Explain why a mutation in a sperm cell could affect a child, but a mutation in a skin cell would not.
Hard
48.Plan an investigation to find out whether the environment affects the height of bean plants. State what you would change, measure and keep the same, and how you would make the results reliable.
Hard
49.Which evidence best shows that a characteristic is influenced by the environment as well as by genes?
Hard
- AAll brothers and sisters have the same blood group
- BChildren usually have the same eye colour as a parent
- CTwo cloned plants grown in the same room look identical
- DIdentical twins brought up in different places differ in mass

Notes de révision

## The big idea - **Variation** is the differences between individuals of a species. It is the raw material for natural selection (**Change**, **Evidence**). ## Types of variation - **Continuous:** any value in a range (height, leaf length). Histogram. - **Discontinuous:** separate categories (blood group). Bar chart. - Use the **mean** and the **range** to summarise continuous data. ## Causes - **Genetic:** different alleles inherited from parents. - **Environmental:** light, food, injury. - **Both:** height. Identical twins share genes, so differences between them are environmental. - **Sexual reproduction** shuffles alleles: random mix in each gamete (about 8 million combinations) and random fertilisation. Asexual offspring are clones. ## Mutations - A **mutation** is a random change in the base sequence of DNA. It makes a new allele. - Rate rises with **ionising radiation** and some **chemicals**. - Only mutations in **gametes** are inherited. - Most are **neutral**, some **harmful**, a few **beneficial**. The **environment** decides (sickle cell and malaria). ## Investigating - Change one variable (light), measure one (height), control the rest. Repeat and use a mean.

Variation: Differences between individuals of the same species.
Continuous variation: A characteristic that can take any value within a range, such as height.
Discontinuous variation: A characteristic that falls into separate categories, such as blood group.
Allele: A version of a gene.
Genetic variation: Differences caused by different alleles inherited from parents.
Environmental variation: Differences caused by conditions during an individual's life.
Gamete: A sex cell (sperm or egg) that carries half the usual number of chromosomes.
Clone: An organism genetically identical to its parent.
Mutation: A random change in the base sequence of DNA.
Ionising radiation: Radiation such as X-rays and gamma rays that damages DNA and raises the mutation rate.
Neutral mutation: A mutation that does not change how the organism looks or works.
Beneficial mutation: A mutation that gives an advantage in the organism's environment.
Mean: The sum of the values divided by the number of values.
Range: The largest value minus the smallest value.

Cartes mémo

What is variation?

The differences between individuals of the same species.

What is continuous variation?

A characteristic that can take any value in a range, such as height or leaf length.

What is discontinuous variation?

A characteristic that falls into separate categories, such as ABO blood group.

Which graph shows continuous data and which shows discontinuous data?

Histogram (touching bars) for continuous; bar chart (gaps between bars) for discontinuous.

What causes genetic variation?

Different alleles inherited from parents.

What causes environmental variation?

Conditions during life, such as light, diet and injury.

Why can identical twins differ as adults?

They have the same genes, so differences are caused by the environment.

How does sexual reproduction cause variation?

Each gamete has a random mix of chromosomes, and any sperm can fertilise any egg.

Why are asexual offspring similar to the parent?

They are clones, made by copying the parent's DNA.

What is a mutation?

A random change in the base sequence of DNA, which can make a new allele.

Name two things that increase the mutation rate.

Ionising radiation (such as X-rays) and some chemicals (such as those in tobacco smoke).

Which mutations can be inherited?

Only those in gametes or the cells that make them.

Why can a mutation change a protein?

The order of bases is a code for amino acids, so a changed base can change an amino acid.

Are most mutations harmful?

No. Most are neutral, some are harmful and a few are beneficial.

How do you calculate a mean?

Add up all the values and divide by how many there are.

How do you calculate a range?

Largest value minus smallest value.

Why does the sickle cell allele stay common where malaria occurs?

One copy protects against malaria, so carriers survive and pass it on.

What makes an investigation reliable?

Using many samples, repeating the test and calculating a mean.

Unlock all 49 questions, flashcards & more

Crée un compte gratuit pour voir toutes les questions, les diapos, les cartes mémo et les notes de révision de ce thème.

S'INSCRIRE — GRATUIT CONNEXION

Annales

Les annales d'entraînement pour ce thème arrivent bientôt.

Bientôt disponible

Height (cm)	Number of pupils
150 to 154	3
155 to 159	8
160 to 164	11
165 to 169	6
170 to 174	2