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D3.2.6—Phenotypic plasticity

Phenotypic plasticity occurs when the same genotype produces different phenotypes under different environmental conditions in inheritance problems in inheritance problems.

Syllabus
First assessment 2025
Objective
D3.2.6
Level
SL

Phenotypic Plasticity Changes Expression, Not Genotype

Phenotypic plasticity is the capacity of one genotype to produce different phenotypes under different environmental conditions.

Environmental signals can change which genes are expressed and how much product is made, altering physiology or form without changing the DNA sequence.

Many plastic responses can reverse during an individual's lifetime if the environment changes again; the inherited genotype remains the same.

The same plant genotype may form broader leaves in shade and smaller leaves in bright, dry conditions because development responds to the local environment.

Plasticity is not mutation and does not guarantee that the acquired phenotype is inherited by offspring.

Phenotypic plasticity

Assessment in practice

1 marks
How it is assessed

This objective is assessed through multiple choice.

What earns marks

Build the answer around this relationship: One genotype can produce different phenotypes in different environments.

Representative question

Question 1

[Maximum number: 1]

Scientists incubated larvae of the moth Utetheisa ornatrix at either 15∘C15^{\circ} \mathrm{C} or 22∘C22^{\circ} \mathrm{C} until they hatched. They found the hatched moths had different wing colour patterns due to phenotypic plasticity.

Moth from larvae incubated at \(15^{\circ

Moth from larvae incubated at \(22^{\circ

Which of the following explains the observed differences in wing colour?

A

Colder temperatures induce mutations in genes for wing colour.

B

The expression of genes for wing colour is affected by temperature.

C

A mutation makes moths less visible to predators in cold climates.

D

Wing colour is the result of polygenic inheritance.

Retrieve the Core Inheritance Route

Core D3.2 is secure when the student can move from allele rules into predictions and evidence: gametes form genotypes, genotypes can produce phenotypes, different dominance patterns need different notation, and pedigrees or plots require evidence-based interpretation.

  • haploid gametes carry one allele and fertilization restores a diploid genotype
  • dominance, codominance, incomplete dominance, environment, and plasticity affect the observed trait
  • PKU, ABO, sex determination, and haemophilia use different inheritance rules and notation
  • pedigrees infer inheritance patterns and box plots summarize continuous variation

Solve Core Inheritance Questions

Core inheritance exam questions reward disciplined reasoning. First identify the inheritance rule, then write the correct notation or evidence, then state the phenotype, ratio, or conclusion. This prevents the common mistake of writing definitions without solving the genetic problem.

  • Use allele and genotype notation correctly for monohybrid, ABO, PKU, haemophilia, and sex-determination contexts.
  • Connect genotype, dominance pattern, environment, or plasticity to phenotype.
  • Use pedigree or box-plot evidence to justify an inheritance or variation conclusion.

Concept essentials

  • One genotype can produce different phenotypes in different environments.
  • Phenotypic plasticity changes expression without changing DNA sequence.
  • Environmental effects can complicate genotype-to-phenotype predictions.