Two causes of variation?
Reveal answer
Genetic (alleles) + environmental (conditions).
Key words: genetic · environmental
4(b) INHERITANCE · RECALL
4.33 Genetic and environmental variation
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Example of continuous variation?
Reveal answer
Height / mass / hand span.
Key words: height
Example of discontinuous variation?
Reveal answer
Blood group / tongue rolling.
Key words: blood group
Why study identical twins?
Reveal answer
Same genes → differences are environmental.
Key words: environmental
Graph for continuous data in classes?
Reveal answer
A histogram (bars touching).
Key words: histogram
Graph for discontinuous data?
Reveal answer
A bar chart with gaps.
Key words: bar chart
Why use cuttings to test environmental effects?
Reveal answer
Clones → genes fixed → only environment varies.
Key words: clones
What is meant by the term variation?
Reveal answer
Differences between individuals in a population.
Key words: variation
What is meant by the term discontinuous variation?
Reveal answer
Variation in distinct categories with no intermediates.
Key words: discontinuous variation
What is meant by the term environmental variation?
Reveal answer
Differences caused by conditions and experiences rather than inherited DNA sequence.
Key words: environmental variation
Sources and patterns of variation, Genetic. Cause? Example?
Reveal answer
Cause: Alleles inherited from parents. Example: ABO blood group.
Key words: Genetic
Sources and patterns of variation, Environmental. Cause? Example?
Reveal answer
Cause: Conditions/experiences. Example: Accent learned from community.
Key words: Environmental
Sources and patterns of variation, Both. Cause? Example?
Reveal answer
Cause: Genotype × environment. Example: Height.
Key words: Both
Sources and patterns of variation, Continuous. Cause? Example?
Reveal answer
Cause: Range of values. Example: Mass or height.
Key words: Continuous
Sources and patterns of variation, Discontinuous. Cause? Example?
Reveal answer
Cause: Separate categories. Example: Blood group.
Key words: Discontinuous
True or false, and why? “Every difference is inherited.”
Reveal answer
False. Some result from environmental conditions or choices.
True or false, and why? “Environmental variation changes genes automatically.”
Reveal answer
False. It can change phenotype without changing DNA sequence.
True or false, and why? “A continuous distribution proves only one cause.”
Reveal answer
False. It often reflects many genes and/or environmental factors.