Practise DNA and the genome. 13 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
What DNA, chromosomes, genes and the genome are, how a gene codes for a protein, and why studying the human genome matters. Expect short recall and 'put these in order of size' questions, plus 2 to 3 mark questions on how the human genome is useful.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
State where DNA is foundThe genetic material in the nucleus is a chemical called DNA, contained in chromosomes.
4
Describe the structure of DNA simplyDNA is a polymer made up of two strands forming a double helix.
4
Put nucleus, chromosome and gene in size orderNucleus (largest), then chromosome, then gene (a small section of DNA on a chromosome).
5
Define gene and genomeA gene is a small section of DNA on a chromosome; the genome is all of an organism's genetic material.
6
Explain how a gene makes a proteinEach gene codes for a particular sequence of amino acids, which makes a specific protein.
6
Give three uses of the human genomeFinding genes linked to disease, understanding and treating inherited disorders, and tracing past human migration.
7
Discuss the importance of the human genomeExplain how each use could benefit people, especially in medicine.
Notes
DNA, chromosomes and genes
The genetic material in the nucleus of a cell is a chemical called DNA.
DNA is a polymer made up of two strands forming a double helix.
DNA is contained in structures called chromosomes. Each chromosome contains one very long molecule of DNA.
A gene is a small section of DNA on a chromosome.
Each gene codes for a particular sequence of amino acids, to make a specific protein. Proteins such as enzymes control the characteristics of the organism.
In order of size: nucleus → chromosome → gene.
The genome
The genome of an organism is the entire genetic material of that organism.
The whole human genome has now been studied. This will be very important for medicine in the future.
Why understanding the human genome matters
Searching for genes linked to different types of disease. People with a higher risk can be tested and treated or advised earlier.
Understanding and treating inherited disorders, such as cystic fibrosis, which could lead to better treatments.
Tracing human migration patterns from the past. Comparing the DNA of people from different parts of the world shows how groups are related and how early humans spread across the Earth.
Cheatsheet
DNA = the genetic material in the nucleus
DNA = a polymer of two strands forming a double helix
Chromosome = structure that contains DNA
Gene = small section of DNA on a chromosome that codes for a particular sequence of amino acids, to make a specific protein
Genome = the entire genetic material of an organism
Human genome uses: genes linked to disease; understanding and treating inherited disorders; tracing past human migration
How to answer each type of question
Recall: complete sentences or define the terms
1 to 4 marks4
Learn a one-line definition of DNA, chromosome, gene and genome.
Watch for distractors in a word box: gene and genome are easy to mix up.
Example. Complete the sentences using words from the box. [ chromosomes / double helix / gene / genome / protein ] DNA is a polymer made of two strands forming a ________. DNA is found in structures called ________. A ________ is a small section of DNA that codes for a specific ________. [4 marks]
Show the model answer
double helix (1); chromosomes (1); gene (1); protein (1)
Explain how a gene controls a characteristic
2 to 3 marks6
A gene is a section of DNA.
It codes for a particular sequence of amino acids.
The amino acids make a specific protein, which affects the characteristic (e.g. an enzyme that makes a pigment).
Example. A gene controls whether a rabbit's fur contains a brown pigment. The pigment is made in a reaction controlled by an enzyme. Explain how the gene controls the colour of the rabbit's fur. [3 marks]
Show the model answer
The gene is a section of DNA that codes for a particular sequence of amino acids (1). This sequence of amino acids makes a specific protein, the enzyme (1). The enzyme controls the reaction that makes the brown pigment, so it decides whether the fur is brown (1).
Give uses of understanding the human genome
2 to 3 marks6
Give one use per mark: genes linked to disease, inherited disorders, human migration.
Add the benefit of each: earlier testing, new treatments, understanding our history.
Check whether the question says 'in medicine': migration is not a medical use.
Example. The whole human genome has been studied. Give two ways this knowledge could be useful in medicine. [2 marks]
Show the model answer
Any two: finding genes linked to diseases, so people at risk can be tested or treated earlier (1); understanding inherited disorders such as cystic fibrosis, so better treatments can be developed (1).
Shortcuts and memory tricks
Think of nesting boxes: the nucleus holds chromosomes, chromosomes are made of DNA, and genes are short sections of that DNA.
Gene = one instruction (for one protein); genome = the whole instruction book.
Uses of the human genome, 'DIM': Disease genes, Inherited disorders, Migration.
Where marks are lost
Saying a gene is bigger than a chromosome. A gene is a small section of the DNA on a chromosome.
Saying a gene codes for 'a characteristic' or for 'an amino acid'. It codes for a sequence of amino acids that makes a specific protein.
Confusing genome (all the genetic material) with gene.
Saying DNA is a single strand. It has two strands forming a double helix.
Exam technique
When asked how a gene affects a characteristic, go through the chain: gene → sequence of amino acids → protein → characteristic.
If asked for uses 'in medicine', don't give tracing human migration.
Use the words polymer and double helix when describing DNA.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
DNA is a polymer made of two strands. What name is given to the shape of a DNA molecule?
Double helix
The whole human genome has now been studied. What is meant by the genome of an organism?
The entire genetic material of that organism
Name the structures in a cell's nucleus that contain most of an organism's DNA.
Chromosomes
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
The genetic material in the nucleus of a cell is found in chromosomes.
(a) What chemical is the genetic material in the nucleus made of? Tick (✓) one box.[1]
DNA
Glucose
Lipid
Starch
(b) DNA is a polymer made of two strands. What name is given to the shape of a DNA molecule?[1]
(c) Write the words chromosome, gene and genome in order of size, starting with the smallest.[1]
(d) What is a gene?[2]
Show the answer and mark scheme
(a)Answer: DNA
(b)Answer: Double helix
double helix
(c)Answer: Gene, chromosome, genome
gene, chromosome, genome
(d)Answer: A small section of DNA on a chromosome that codes for a particular sequence of amino acids, to make a specific protein
a (small) section of DNA (on a chromosome)
that codes for a particular sequence of amino acids / a specific protein
Question 2Medium7 marks
The whole human genome has now been studied.
(a) What is meant by the genome of an organism?[1]
(b) Give three reasons why studying the human genome is important.[3]
(c) Scientists found that women with a particular allele of one gene have a much higher risk of developing breast cancer. Suggest how this discovery could be used to help people.[2]
(d) Suggest one concern that people may have about genetic testing.[1]
Show the answer and mark scheme
(a)Answer: The entire genetic material of that organism
the entire / all the genetic material of the organism
(b)Answer: To search for genes linked to different types of disease; to understand and treat inherited disorders; to trace human migration patterns from the past
searching for genes linked to (different types of) disease
understanding and treatment of inherited disorders
tracing human migration patterns from the past
(c)Answer: Women could be tested for the allele; those with it could have more frequent check-ups or preventive treatment so any cancer is found early; drugs could be developed that target the faulty protein
people can be tested / screened for the allele
people with the allele can have regular check-ups / screening so cancer is detected early
people with the allele could choose preventive treatment / make lifestyle changes
new treatments / drugs could be developed that target the effects of the allele
(d)Answer: Insurance companies or employers might discriminate against people with a high-risk allele
discrimination by insurers / employers / anxiety about a result for a disease that may never develop / privacy of genetic data
Question 3Hard8 marks
Scientists compared the same section of DNA, 1000 bases long, in people from four populations, W, X, Y and Z. {table} shows the number of bases that were different between each pair of populations.
[object Object]
(a) Which two populations are most closely related? Give a reason for your answer.[2]
(b) Differences in DNA build up over time because mutations happen continuously. Explain how comparing DNA can show how long ago two populations separated.[2]
(c) Scientists think that populations X, Y and Z are all descended from people who migrated away from population W. Explain how the data support this idea.[2]
(d) Tracing human migration is one reason why the human genome is studied. Give two other reasons.[2]
Show the answer and mark scheme
(a)Answer: Y and Z: they have the fewest differences (3 bases)
Y and Z
fewest differences in their DNA (3)
(b)Answer: After populations separate, each collects different mutations; the more differences there are, the longer ago they shared a common ancestor
after separating, different mutations build up in each population
more differences means they separated longer ago / shared a common ancestor longer ago
(c)Answer: W is the most different from each of the other populations (12 or 13 differences), while X, Y and Z differ from each other by only 3 to 8 bases, so X, Y and Z share a more recent common ancestor
W has the most differences from each of the other populations (12–13)
X, Y and Z are more similar to each other (3–8 differences) so they share a more recent common ancestor (the migrants)
(d)Answer: Searching for genes linked to diseases; understanding and treating inherited disorders
searching for genes linked to (different types of) disease