Explain how alleles pass to offspring
Individuals do not evolve a needed allele; inherited alleles pass through reproduction.
Section 18.3 · Selection
Core and Extended; Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Use the stated case, sample and assumptions. Diagrams and numerical records in this pathway are original teaching models; written answers are self-checked.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
How do parents pass alleles to the next generation?
What you will learn
- Trace allele transmission from parents to offspring
- Explain a population change without assigning intention
Original selection schematic. Population counts and scenarios are supplied teaching models; they are not field observations.
| Stage or record | Meaning |
|---|---|
| Stated inheritance | Feature linked to an inherited allele |
| Outcome | One group leaves more offspring in this case |
| Transmission | Parents pass alleles to descendants |
| Not calculated | Allele frequency from phenotype alone |
Trace allele transmission from parents to offspring
Alleles are versions of genetic information. During reproduction, parents pass alleles to offspring. If a case states that a feature is inherited, individuals with that feature can contribute the relevant alleles to the next generation. The alleles are transmitted through reproduction; they are not sent because a parent needs a feature.
Suppose a stated bird population contains an inherited beak feature that improves access to the only seed type after a seasonal change. If birds with that feature produce more offspring in that setting, more offspring may inherit the associated allele. The explanation depends on the supplied inheritance link, reproductive outcome and the next generation record.
Explain a population change without assigning intention
Do not confuse an allele with a visible phenotype. A phenotype count may include different genotypes, depending on the inheritance pattern. Unless the problem provides the genotypes and rules, do not calculate an allele frequency from appearances. Cambridge’s requirement here is to describe that adapted individuals pass their alleles to the next generation.
The population changes over generations as some inherited variants contribute more offspring than others. The parent individuals do not change their alleles during life in response to a need. Natural selection acts through differences in reproductive contribution; alleles are carried forward by descendants, and the pattern can be checked in later generations.
Pause and explain
A case gives an inherited allele–feature link and says one group leaves more offspring. What follows?
Worked example
A case states an inherited beak allele is linked to a feature that helps birds open hard seeds. Birds with the feature leave more offspring. Complete the chain to the next generation.
Show the worked solution
- Use the supplied inheritance link between the feature and the allele.
- Parents pass alleles to offspring during reproduction; more offspring from that group can carry the allele.
Answer The better-reproducing birds can pass the stated allele to more offspring. The case does not imply that individual birds changed their alleles or that phenotype counts alone reveal every genotype.
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.
A stated inherited seed-opening feature is present in 12 birds; those birds produce 30 of the next generation’s 50 offspring. What can be concluded?
Give me a hint
Use the supplied inheritance link and count the offspring contribution.
Compare my reasoning
- The feature group contributes 30 of the 50 offspring.
- That is 60% of the next generation’s recorded offspring.
The group contributed 60% of the recorded offspring and can pass the linked allele to descendants; the count is not an allele-frequency estimate without genotype information.
Look for these in your work
- Correct offspring denominator
- Transmission distinguished from frequency
A student says, “The cold made each parent grow thicker feathers, then it passed the change to its chicks.” Correct the selection explanation.
Give me a hint
Separate an individual change from inherited differences and reproduction.
Compare my reasoning
- The case needs pre-existing or otherwise evidenced inherited variation.
- Parents pass alleles through reproduction; the environment does not direct a needed allele.
The explanation should say that individuals with relevant inherited variation may leave more offspring in the cold context, passing those alleles to descendants.
Look for these in your work
- Individual change corrected
- Alleles transmitted through offspring
An inherited phenotype is dominant in a supplied model, but genotypes are not counted. Why should you avoid using phenotype percentage as allele percentage?
Give me a hint
More than one genotype may produce the same phenotype.
Compare my reasoning
- The supplied inheritance rule can group genotypes under one appearance.
- Without genotype counts and stated assumptions, allele copies are not measured.
A phenotype percentage describes appearances, not automatically allele copies; the genotype model and counts are needed for an allele-frequency calculation.
Look for these in your work
- Genotype–phenotype distinction
- Evidence requirement
Common mistakes
- Saying need makes a new allele appear
- Equating phenotype counts with allele frequencies without genotype rules
- Saying only parents with the feature can reproduce
What can you explain now?
A case gives an inherited allele–feature link and says one group leaves more offspring. What follows?
Compare with the explanation
That group can pass the linked allele to more offspring
More offspring can carry inherited alleles from those parents.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Without your notes, trace allele transmission from parents to offspring and explain a population change without assigning intention. Explain the mechanism, use the given population or breeding records and state what the evidence does not establish.
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.