Lesson 7 of 7 / Inheritance and genetic problems
Genes, diet and continuous variation
Why can similar genotypes produce different developmental outcomes?
I can explain environmental effects, honeybee differentiation and patterns of variation.
I can link genotype to phenotype.Syllabus
Syllabus 9477, Core 2(w). Link genotype to phenotype.
I can explain environmental effects on phenotype, including honeybee diet.Syllabus
Syllabus 9477, Core 2(bb). Explain environmental effects on phenotype, including honeybee diet.
I can distinguish continuous and discontinuous genetic variation.Syllabus
Syllabus 9477, Core 2(cc). Distinguish continuous and discontinuous genetic variation.
About 7 min
Make a guess. You are not marked.
Queen and worker honeybees can develop from genetically similar female larvae. What mainly decides which one a larva becomes?
Show the answer
Its diet as a larva.
Sustained royal-jelly feeding promotes queen development by changing gene expression, not the DNA sequence.
The key idea
Phenotype can reflect both genotype and environment; many additive genes often produce a continuous range rather than distinct categories.
Build from gametes
How can diet change development without changing alleles?
Sustained abundant royal-jelly feeding promotes queen development, including reproductive specialisation. This illustrates environmental regulation of phenotype. It does not identify one universally sufficient food molecule or require diet to rewrite the DNA sequence.
Original simplified developmental comparison. To establish a diet effect experimentally, compare similar-aged larvae with controlled genetic background and other rearing conditions, with replication. Continuous traits such as height instead require measurements across a range; discrete castes are not a bell-shaped height distribution.
Explanation
Continuous variation shows a range of values with many intermediates, such as body height. Many genes with additive effects can contribute small increments, and environmental factors such as nutrition can widen or shift the distribution. A roughly normal distribution can result, but a bell shape is not a requirement for every continuous trait.
Discontinuous variation has distinct categories, often associated with one or a few genes, such as the simplified ABO phenotypes. Genetic control does not mean environmental effects are impossible; the appropriate classification concerns the observed pattern and underlying model.
Female honeybee larvae can develop into queens or workers depending strongly on their nutritional environment, including sustained abundant royal-jelly feeding that promotes queen development, compared with the worker rearing diet. This is a dietary and developmental interaction, not proof that one food molecule alone determines caste. Nutrition affects signalling and gene expression, contributing to differences in growth, reproduction and morphology. It does not require all queen-specific genes to be absent from workers.
An environmental effect on phenotype is not automatically inherited as a DNA mutation. To investigate genetic and environmental contributions, compare related genotypes across controlled environments and use replication. A correlation between diet and phenotype alone can be confounded by other differences unless the design addresses them.
Step by step
- 1
Describe the pattern
Range with intermediates or distinct classes?
- 2
Separate genetic and environmental contributions
Do not equate continuous with non-genetic.
- 3
Use a comparison design
Control genotype or environment where possible.
Worked example
Work through the evidence
Genetically similar plant groups grown with two nutrient levels differ in mean height, with variation within each group. Explain.
One way to explain it
Nutrient conditions influence growth, shifting the phenotype distribution. Remaining variation can reflect genetic differences and other environmental or random developmental effects.
Why this answer works
- Mean differences need replication and statistical evaluation.
- A nutrient effect does not show genes are irrelevant.
Watch out for this
A student says: "A continuous trait is caused only by the environment." What is wrong with this?
Show the answer
Many continuous traits reflect additive effects of multiple genes as well as environment.
Check your understanding
What does queen/worker differentiation illustrate?
Show the answer
An environmental input can influence gene expression and phenotype.
Developmental nutrition affects the pathway taken by genetically capable larvae.
Quick recall
Why can similar genotypes produce different developmental outcomes?