The Understanding of Genetics
Master The Understanding of Genetics for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Understand how Gregor Mendel's work with pea plants laid the foundations of genetics long before genes were discovered.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Understanding of genetics developed gradually, and two scientists are required: Gregor Mendel and the later scientists who identified DNA's structure.
Mendel carried out breeding experiments on pea plants in the mid-nineteenth century. He concluded that inheritance is determined by units passed on unchanged, that these units are inherited separately, and that some units are dominant over others. He was, in effect, describing genes and alleles before either word existed.
His work was not recognised at the time because the significance was not appreciated and chromosomes had not yet been observed. Only in the early twentieth century, when behaviour of chromosomes during cell division was observed, was the link made — and Mendel's units were finally understood as genes.
Revision notes
Mendel's conclusions
Inheritance is determined by units that are passed on from both parents unchanged.
These units are inherited separately from one another. Some units are dominant over others. He was describing genes and alleles, though those terms did not exist.
Why his work was overlooked
The significance of his work was not appreciated at the time.
Chromosomes had not yet been observed, so there was no known structure that could carry his units. His work was published but largely ignored for decades.
How the picture came together
In the early twentieth century, behaviour of chromosomes during cell division was observed.
It was noted that chromosomes and Mendel's units behaved in similar ways, so the units — now called genes — were shown to be located on chromosomes. Later, DNA's structure was determined and the mechanism of inheritance was finally understood.
Key points
- Mendel carried out breeding experiments on pea plants.
- He concluded inheritance is determined by separately inherited units.
- He found some units are dominant over others.
- His work was not recognised until after his death.
- Chromosomes had not been observed in his lifetime.
- Mendel's units were later identified as genes.
Worked examples
Example 1
State two conclusions Mendel reached from his experiments. [2 marks]
Model answer
That inheritance is determined by units passed on from both parents unchanged (1 mark), and that some units are dominant over others (1 mark).
Example 2
Explain why Mendel's work was not recognised during his lifetime. [2 marks]
Model answer
The significance of his work was not appreciated at the time (1 mark), and chromosomes had not yet been observed, so there was no known structure that could carry the units he described (1 mark).
Example 3
Explain how scientists later linked Mendel's units to chromosomes. [2 marks]
Model answer
In the early twentieth century the behaviour of chromosomes during cell division was observed (1 mark), and scientists noticed that chromosomes and Mendel's units behaved in very similar ways, so the units were shown to be located on the chromosomes (1 mark).
Common mistakes
Saying Mendel discovered DNA.
He described units of inheritance. DNA's structure was determined much later.
Saying his work was rejected as wrong.
It was not rejected but simply not appreciated, because the supporting evidence did not yet exist.
Using the word gene for Mendel's own terminology.
He called them units; the term gene came later.
Giving only one conclusion when two are asked for.
Read the mark allocation.
Exam tips
- Learn Mendel's three conclusions.
- Explain the delay in terms of chromosomes not yet being observed.
- Use the word units when describing Mendel's own findings.
- Link the eventual understanding to observations of cell division.
Key terms
- Mendel
- The scientist whose pea plant experiments established the basis of genetics.
- Unit of inheritance
- Mendel's term for what is now called a gene.
- Dominant
- A characteristic expressed when only one copy of the unit is present.
- Chromosome
- The structure later shown to carry genes.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.