Chi-square practice problems

Biology Unit 5. Try each one, then open the worked solution. The Credit Sprint app generates unlimited new versions with fresh numbers.

Problem 1.

A monohybrid cross is expected to give a 3:1 ratio. Out of 400 offspring, 296 show the dominant trait and 104 the recessive trait. Calculate χ².

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Expected 300 and 100. χ² = (296−300)²/300 + (104−100)²/100 = 0.053 + 0.16 = 0.21.

Problem 2.

A monohybrid cross is expected to give a 3:1 ratio. Out of 200 offspring, 138 show the dominant trait and 62 the recessive trait. Calculate χ².

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Expected 150 and 50. χ² = (138−150)²/150 + (62−50)²/50 = 0.96 + 2.88 = 3.84.

Problem 3.

A monohybrid cross is expected to give a 3:1 ratio. Out of 200 offspring, 145 show the dominant trait and 55 the recessive trait. Calculate χ².

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Expected 150 and 50. χ² = (145−150)²/150 + (55−50)²/50 = 0.167 + 0.5 = 0.67.

Problem 4.

A monohybrid cross is expected to give a 3:1 ratio. Out of 200 offspring, 135 show the dominant trait and 65 the recessive trait. Calculate χ².

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Expected 150 and 50. χ² = (135−150)²/150 + (65−50)²/50 = 1.5 + 4.5 = 6.

Problem 5.

A monohybrid cross is expected to give a 3:1 ratio. Out of 100 offspring, 72 show the dominant trait and 28 the recessive trait. Calculate χ².

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Expected 75 and 25. χ² = (72−75)²/75 + (28−25)²/25 = 0.12 + 0.36 = 0.48.

Problem 6.

A monohybrid cross is expected to give a 3:1 ratio. Out of 200 offspring, 145 show the dominant trait and 55 the recessive trait. Calculate χ².

Show solution

Expected 150 and 50. χ² = (145−150)²/150 + (55−50)²/50 = 0.167 + 0.5 = 0.67.