What is meant by the term polygenic?
Reveal answer
Influenced by alleles at several gene loci.
Key words: polygenic
4(b) INHERITANCE · RECALL
4.22 Polygenic inheritance
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What is meant by the term continuous variation?
Reveal answer
Variation across a measurable range with many intermediate values.
Key words: continuous variation
What is meant by the term monogenic?
Reveal answer
Mainly controlled by one gene locus in the model.
Key words: monogenic
What is meant by the term distribution?
Reveal answer
Pattern of values and their frequencies in a dataset.
Key words: distribution
Inheritance and variation patterns: for Number of main loci, give the monogenic model and the polygenic model.
Reveal answer
Monogenic model: One. Polygenic model: Many.
Key words: Number of main loci
Inheritance and variation patterns: for Phenotype categories, give the monogenic model and the polygenic model.
Reveal answer
Monogenic model: Often discrete. Polygenic model: Often continuous.
Key words: Phenotype categories
Inheritance and variation patterns: for Expected ratios, give the monogenic model and the polygenic model.
Reveal answer
Monogenic model: Simple ratios may apply. Polygenic model: Many combinations blur ratios.
Key words: Expected ratios
Inheritance and variation patterns: for Environmental influence, give the monogenic model and the polygenic model.
Reveal answer
Monogenic model: Can occur. Polygenic model: Often substantial.
Key words: Environmental influence
Inheritance and variation patterns: for Example, give the monogenic model and the polygenic model.
Reveal answer
Monogenic model: ABO group. Polygenic model: Height.
Key words: Example
True or false, and why? “A polygenic trait has one dominant allele.”
Reveal answer
False. Many loci contribute, so simple dominance at one locus cannot describe the whole trait.
True or false, and why? “Continuous variation is caused only by environment.”
Reveal answer
False. It can arise from many genes plus environmental effects.
True or false, and why? “Genes determine an exact fixed height.”
Reveal answer
False. They influence potential, while environment and development modify outcome.
Give an example of a human characteristic controlled by several genes.
Reveal answer
Skin colour (also height and eye colour).
Key words: skin colour
Why does polygenic inheritance give continuous variation?
Reveal answer
Many genes each add a small effect → many combinations → a smooth range of phenotypes.
Key words: range
What shape of graph does a polygenic characteristic usually give?
Reveal answer
A bell-shaped (normal distribution) curve, plotted as a histogram.
Key words: bell