AQA GCSE Biology (8461), Higher tier · Inheritance, variation and evolution › Understanding of genetics and evolution
Practise The understanding of genetics. 11 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.
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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
Question 3Hard7 marks
The gene theory was developed through the work of many scientists over about 100 years.
(a) In the late 19th century, scientists observed how chromosomes behave during cell division. In the early 20th century, scientists concluded that Mendel's 'units' are located on chromosomes. Explain how comparing the behaviour of chromosomes with Mendel's results led to this conclusion.[3]
(b) In the mid-20th century the structure of DNA was determined and the way genes work was discovered. Explain why this was important for the gene theory.[2]
(c) Suggest why it took many scientists, working over many years, to develop the gene theory.[2]
Show the answer and mark scheme
(a)
Mendel's units and chromosomes are both found in pairs
the members of each pair separate when gametes / sex cells are formed, so each gamete has one of each pair
at fertilisation the pairs are restored / offspring receive one of each pair from each parent
(so) chromosomes and units behave in the same way, suggesting that the units are carried on chromosomes
(b)
it showed what genes are made of / that genes are sections of DNA
it explained how genes control characteristics / how genes code for proteins / how genes are copied and passed on
(c)
new technology (e.g. better microscopes) was needed to observe chromosomes / DNA
each discovery built on earlier discoveries / new evidence had to be collected
ideas had to be tested / repeated / checked by other scientists
earlier work (e.g. Mendel's) was not widely known or accepted