Recognise sexual self-fertilisation with one adult
Use nuclear fusion rather than adult count.
Section B15.2 · Sexual reproduction
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall DNA, inherited characteristics, nuclei and the distinction between growth and reproduction.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Can a one-adult record still describe sexual reproduction?
What you will learn
- Distinguish two gametes from two adults
- Apply the definition to self-fertilisation
Recognise sexual self-fertilisation with one adult
| Feature | Meaning |
|---|---|
| Adult count | May be one in self-fertilisation |
| Gamete count | Two nuclei contribute |
| Mechanism | Fusion remains fertilisation |
| Contrast | Vegetative cutting follows a different origin |
Distinguish two gametes from two adults
Some organisms can provide both gametes from one adult individual. In a supplied self-fertilisation record, the nuclei of those gametes fuse and form a zygote. This is sexual reproduction despite only one adult being involved. The key count in the definition is two gametes whose nuclei fuse, not a universal requirement for two separate adults.
For a plant example, a supplied history may state that both gamete contributions originated from the same plant. That origin does not turn nuclear fusion into vegetative cloning. A runner or cutting forms a new plant by a different route without the supplied gamete fusion. Classify the particular event rather than assigning one mode to every offspring of the species.
Apply the definition to self-fertilisation
Self-fertilisation can limit the new genetic contributions introduced from different adults compared with a cross between different individuals. It still includes a sexual fusion event, and may yield different inherited combinations where the parent carries different versions of genes. Do not assume either that every self-fertilised offspring is a clone or that its variation always matches every cross.
A picture of one adult with offspring is insufficient to distinguish self-fertilisation, vegetative copying and other possible histories. The question must supply the relevant origin evidence. Later plant lessons distinguish pollination routes and their consequences in more detail. This lesson establishes the definition boundary without claiming that all organisms self-fertilise or that every seed proves nuclear fusion.
Sources for this lesson
Pause and explain
Which evidence distinguishes the supplied self-fertilisation from a cutting?
Worked example
One plant supplies two gametes whose nuclei fuse. Is the event sexual or asexual?
Show the worked solution
- Both gametes originate from one adult.
- Their nuclear fusion is the decisive event.
Answer Sexual self-fertilisation.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Classify a supplied one-plant event with two gamete nuclei fusing.
Give me a hint
Use the fusion definition.
Compare my reasoning
- Two gametes are supplied.
- Their nuclei fuse.
It is sexual reproduction by self-fertilisation, despite one adult plant being involved.
Look for these in your work
- Name sexual self-fertilisation
- Use nuclear fusion evidence
Explain why a self-fertilised seed and a rooted cutting from the same adult differ in origin.
Give me a hint
Compare gamete fusion with vegetative development.
Compare my reasoning
- The seed history supplies nuclear fusion.
- The cutting history supplies vegetative copying.
The supplied seed arises after gamete-nucleus fusion; the cutting develops from vegetative tissue without that fusion.
Look for these in your work
- Compare both histories
- Do not classify by adult count
A photo shows one adult and three similar offspring, with no reproductive history. Can all three be established as clones?
Give me a hint
Appearance and adult count do not establish mechanism.
Compare my reasoning
- The fusion or vegetative origin is not supplied.
- Genetic identity is not tested by resemblance.
No. One visible adult and similar offspring do not establish asexual origin or whole-genotype identity; a reproductive history or genetic evidence is needed.
Look for these in your work
- State the observation limit
- Identify stronger evidence
Common mistakes
- Counting adults instead of gametes and nuclei.
- Treating all offspring of one adult as clones.
What can you explain now?
Which evidence distinguishes the supplied self-fertilisation from a cutting?
Compare with the explanation
Fusion of gamete nuclei
That is absent from the stated vegetative cutting route.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Explain sexual self-fertilisation and why counting adults is insufficient.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.