"Incomplete penetrance" describes a situation where

Answer: Some individuals with a particular genotype do not show the expected phenotype Some genotypes don't always produce the expected phenotype due to environmental modifiers, modifier genes, or chance.

Variable expressivity means

Answer: Individuals with the same genotype show different degrees / forms of the phenotype Same genotype, different phenotype severity (e.g., neurofibromatosis can range from mild skin spots to severe tumors).

The continuous (bell-shaped) distribution of human height is best explained by

Answer: Polygenic inheritance — multiple genes contribute additively, plus environmental effects Many genes each contributing small effects (plus nutrition and environment) produce continuous variation rather than discrete categories.

AP Biology · Topic 5.5

Environmental Effects on Phenotype Practice

Part of Heredity.(IST-1.G)

Practice questions

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Sample questions

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Sample 1difficulty 3/5
$"Incomplete penetrance" describes a situation where$
- A
  $An individual's phenotype is determined entirely by environment, not genotype$
- B
  $Every individual with a particular genotype always shows the expected phenotype$
- C
  $Some individuals with a particular genotype do not show the expected phenotype$
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- D
  $Mutations arise at unusually high frequency at a particular gene locus$
Why
$Some genotypes don't always produce the expected phenotype due to environmental modifiers, modifier genes, or chance.$
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Sample 2difficulty 3/5
$Variable expressivity means$
- A
  $All individuals with the same genotype display an identical phenotypic outcome$
- B
  $Both alleles at a gene locus are silenced through epigenetic modifications$
- C
  $Individuals with the same genotype show different degrees / forms of the phenotype$
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- D
  $The genotype of an individual changes spontaneously over the course of a lifetime$
Why
$Same genotype, different phenotype severity (e.g., neurofibromatosis can range from mild skin spots to severe tumors).$
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Sample 3difficulty 3/5
$The continuous (bell-shaped) distribution of human height is best explained by$
- A
  $Sex-linked inheritance — height genes are located on the X chromosome alone$
- B
  $A single gene with two alleles producing tall and short phenotypes only$
- C
  $Codominance — both alleles fully express to give intermediate height values$
- D
  $Polygenic inheritance — multiple genes contribute additively, plus environmental effects$
  check_circle
Why
$Many genes each contributing small effects (plus nutrition and environment) produce continuous variation rather than discrete categories.$
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