What causes variation between organisms, and what effect do mutations have?
Describe how most phenotypes result from multiple genes, the genetic and environmental causes of variation, the outcomes of the Human Genome Project, and that variation arises through mutations.
A focused answer to Edexcel GCSE Biology 3.19 to 3.23, covering polygenic inheritance, the genetic and environmental causes of variation, the outcomes of the Human Genome Project, and how mutations create variation.
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What this dot point is asking
Edexcel statements 3.19 to 3.23 want you to state that most phenotypic features result from several genes rather than one, describe the genetic and environmental causes of variation, discuss the outcomes of the Human Genome Project, and explain that variation arises through mutations, most of which have little or no effect.
Most features come from many genes
Genetic and environmental variation
Many characteristics are caused by both genes and environment together. A person's height is influenced by their genes but also by their diet as they grow; a plant's leaf size depends on its alleles but also on light, water and minerals.
Mutations
A mutation may change the amino acid order of a protein, which can change the protein's shape and how it works. However:
- Most mutations have no effect on the phenotype, often because they are in non-coding DNA or do not change the protein enough to matter.
- Some have a small effect.
- Rarely, a single mutation has a large effect, which may be harmful, neutral, or occasionally beneficial. Beneficial mutations are the raw material for evolution by natural selection.
The Human Genome Project
The Human Genome Project was an international effort that worked out the sequence of all the bases in the human genome. Its outcomes have wide uses in medicine: predicting and preventing inherited diseases, developing new and more effective medicines tailored to a person's genes, and tracing human ancestry and migration. It also raises issues about privacy and the use of genetic information.
Try this
Q1. Give one example of a purely genetic feature and one purely environmental feature. [2 marks]
- Cue. Genetic: natural eye colour or blood group. Environmental: a scar, a suntan, or a learned language.
Q2. State why most mutations do not change an organism's phenotype. [1 mark]
- Cue. They occur in non-coding DNA or do not change the resulting protein enough to alter the characteristic.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20184 marksVariation between individuals can be genetic or environmental. Explain, with examples, the difference between genetic and environmental causes of variation.Show worked answer →
A 4-mark explain question rewards a clear distinction plus correct examples.
Genetic variation is caused by differences in the alleles an organism inherits, for example natural eye colour or blood group, which are determined entirely by genes.
Environmental variation is caused by the surroundings and lifestyle, for example a scar, a spoken language, or a plant being smaller because it had less light. Many features, such as human height or body mass, are caused by both genes and the environment together.
Markers reward the definition of each, one correct example of each, and ideally the point that many features are both. Putting a purely genetic feature (like blood group) in the environmental column loses marks.
Edexcel 20213 marksExplain how a mutation in the DNA of a body cell can lead to variation, and why most mutations have no effect.Show worked answer →
A 3-mark explain question rewards linking mutation to the protein and phenotype.
A mutation is a random change in the base sequence of DNA. It can change the amino acid sequence of a protein, which may change the protein's shape and function, producing a new characteristic (variation).
Most mutations have no effect because they occur in non-coding DNA, or they do not change the protein enough to alter the phenotype. Only rarely does a single mutation significantly affect the phenotype.
Markers reward mutation as a change in DNA bases, the possible effect on a protein, and the point that most have little or no effect. Saying every mutation is harmful is incorrect.
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Sources & how we know this
- Pearson Edexcel GCSE (9-1) Biology (1BI0) specification — Pearson (2016)