AQA GCSE Biology Foundation (8461), Foundation tier · Inheritance, variation and evolution › Understanding of genetics and evolution
Practise The understanding of genetics. 5 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
How our understanding of inheritance developed: Mendel's experiments on pea plants, the link between his 'units' and chromosomes, and the discovery of the structure of DNA. This is in GCSE Biology only, not in Combined Science. Questions test the order of events and why Mendel's work was not recognised in his lifetime.
Key facts
Mendel: mid-19th century, breeding experiments on pea plants
Mendel's 'units' (now called genes) are passed on to descendants unchanged
Late 19th century: behaviour of chromosomes during cell division observed
Early 20th century: 'units' (genes) are located on chromosomes
Mid-20th century: structure of DNA determined; how genes work explained
Mendel not recognised in his lifetime: no knowledge of chromosomes, genes or DNA; his work was little read
Notes
Mendel's experiments
In the mid-19th century, Gregor Mendel carried out breeding experiments on pea plants.
He crossed plants with different characteristics (e.g. tall and short stems) and counted the offspring with each characteristic over several generations.
One of his observations was that the inheritance of each characteristic is determined by 'units' that are passed on to descendants unchanged. We now call these units genes.
From 'units' to gene theory
diagram
Late 19th century: the behaviour of chromosomes during cell division was observed.
Early 20th century: scientists saw that chromosomes and Mendel's 'units' behaved in similar ways. This led to the idea that the units, now called genes, were located on chromosomes.
Mid-20th century: the structure of DNA was determined and the mechanism of gene function was worked out.
This scientific work by many scientists led to the gene theory being developed.
From Mendel's 'units' to gene theory.
Why Mendel's work was not recognised
The importance of Mendel's discovery was not recognised until after his death.
Chromosomes, genes and DNA were unknown, so there was no mechanism to explain his 'units'.
His work was published in a little-known journal, and he was not a well-known scientist, so few people read it or saw its importance.
This shows how scientific theories develop over time as new evidence is found.
How to answer each type of question
Put the discoveries in order
2 marksGrade 5
Mendel's breeding experiments came first (mid-19th century).
Then chromosomes were seen during cell division (late 19th century).
Then genes were linked to chromosomes (early 20th century).
The structure of DNA came last (mid-20th century).
Example. Put these events in order, starting with the earliest. A The structure of DNA was worked out. B Mendel carried out breeding experiments on pea plants. C Scientists suggested that Mendel's 'units' are located on chromosomes. D The behaviour of chromosomes during cell division was observed. [2 marks]
Show the model answerHide the model answer
B, D, C, A. All four in the correct order (2); two in the correct positions (1).
Don’t lose marks
Saying Mendel discovered genes, chromosomes or DNA. He described 'units' of inheritance; the word 'gene' came later.
Putting the structure of DNA before the link between genes and chromosomes.
Saying Mendel's work was ignored because it was wrong. His results were correct, but they could not be explained at the time.
More tips
Memory tricks
One step per period: mid-1800s Mendel's units → late 1800s chromosomes seen → early 1900s genes on chromosomes → mid-1900s DNA structure.
Mendel = peas and 'units' (units = genes).
Why not recognised? Nobody knew the mechanism, and few people read his work.
Exam technique
Learn the order of events by period; ordering questions are common.
When asked why an idea was not accepted, think: no mechanism, not enough evidence, not widely known.
Link this topic to how science works: theories develop as many scientists find new evidence.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Name Mendel and the plants he usedGregor Mendel carried out breeding experiments on pea plants in the mid-19th century.
Grade 4
State Mendel's key observationThe inheritance of each characteristic is determined by 'units' that are passed on to descendants unchanged.
Grade 5
Put the development of gene theory in orderMendel's units, chromosomes seen in cell division, units linked to chromosomes, then the structure of DNA.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Mendel observed that the inheritance of each characteristic is determined by ‘units’ that are passed on to offspring unchanged. What do we now call these units?
Genes
Mendel crossed pure-breeding pea plants that produced round seeds with pure-breeding plants that produced wrinkled seeds. All of the offspring plants produced round seeds. The allele for round seeds (R) is dominant to the allele for wrinkled seeds (r). Give the genotype of the offspring plants.
Rr
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Our understanding of genetics developed over about 100 years, starting with the work of Gregor Mendel in the mid-19th century.
(a) Mendel carried out breeding experiments. Which type of organism did he use? Tick (✓) one box.[1]
Bacteria
Fruit flies
Mice
Plants
(b) Mendel observed that the inheritance of each characteristic is determined by ‘units’ that are passed on to offspring unchanged. What do we now call these units?[1]
(c) Three later discoveries are given. X The structure of DNA was worked out. Y The behaviour of chromosomes during cell division was observed. Z Scientists realised that genes are located on chromosomes. Write the letters X, Y and Z in the order in which the discoveries were made.[2]
(d) Give one reason why the importance of Mendel’s work was not recognised until after his death.[1]
Show the answer and mark scheme
(a)Answer: Plants
(b)Answer: Genes
genes
(c)Answer: Y, Z, X
Y first
Z before X
(d)
his work was published in a little-known journal / was not widely read
other scientists did not understand his (mathematical) work
genes / chromosomes / DNA had not been discovered, so there was no mechanism to explain his results
he was not a well-known scientist
Question 2Medium6 marks
Gregor Mendel carried out breeding experiments on pea plants for about eight years. Pea flowers normally pollinate themselves. In his experiments, Mendel:
used plants that were ‘pure-breeding’, so that they always produced offspring like themselves
removed the male parts of each flower before they were mature, then used a brush to transfer pollen from a plant he had chosen
covered the flowers with small bags after pollinating them
studied characteristics that had two clearly different forms, such as tall stems or short stems
grew and recorded thousands of plants.
(a) Explain why Mendel removed the male parts of the flowers and then covered the flowers with bags.[2]
(b) Suggest why Mendel studied characteristics with two clearly different forms, rather than characteristics such as the mass of the seeds.[1]
(c) Explain why Mendel grew thousands of plants.[2]
(d) Suggest one reason why pea plants were a good choice for Mendel’s experiments.[1]
Show the answer and mark scheme
(a)
removing the male parts stopped the flowers pollinating themselves
the bags stopped pollen from other plants (carried by insects or wind) reaching the flowers, so Mendel knew which plants were the parents
(b)
each plant could be placed in one group or the other without doubt, so the offspring could be counted / seed mass varies continuously
(c)
which gametes fuse is a matter of chance, so small samples could give misleading ratios
large numbers give ratios closer to the true / expected ratio, so patterns (e.g. 3 : 1) can be seen clearly
(d)
they produce many seeds / offspring
they grow quickly / produce a new generation every year
they are easy to grow
they have many characteristics with two clear forms
they can be self-pollinated or cross-pollinated in a controlled way