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IB Biology HL D3.2.21 Hl Chi Squared Test Questions

Interpret chi-squared tests of genetic ratios using observed and expected counts, degrees of freedom and the 0.05 significance threshold in IB Biology HL D3.2.21.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Use observed and expected genetic counts to interpret a chi-squared result against the expected inheritance ratio.
  • Apply degrees of freedom, the p = 0.05 critical value or p value to decide whether deviation from the expected ratio is statistically significant.

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Study D3.2.21 (HL)—Chi-squared test conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

IB Biology HL D3.2.21 Hl Chi Squared Test Questions question 1

[Maximum number: 2]

The diagram shows one of Thomas Hunt Morgan's crosses of Drosophila in the early 20th century.

Figure for Question IB Biology HL D3.2.21 Hl Chi Squared Test Questions question 1 — IB Biology HL

The chi-squared value was calculated as shown. Deduce, with reasons, whether the observed ratio differed significantly from the expected Mendelian ratio.

c2=Σ( Observed − Expected )2 Expected =1002.6c^{2}=\Sigma \frac{(\text { Observed }- \text { Expected })^{2}}{\text { Expected }}=1002.6
Table for Question IB Biology HL D3.2.21 Hl Chi Squared Test Questions question 1 — IB Biology HL
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