Mendelian Genetics

AP Biology· difficulty 2/5

A monohybrid cross of heterozygous tall (Tt) pea plants produced 600 F1 offspring. Observed counts: 460 tall, 140 short. Expected 3:1 ratio yields 450 and 150. Chi-square = 0.89 (df = 1, critical = 3.84).

Pheno Obs Exp (O-E)²/E Tall 460 450 0.22 Short 140 150 0.67

What conclusion is appropriate?

  • A

    Fail to reject the null; data fit a 3:1 ratio.

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  • B

    Reject the null; the F1 are not heterozygous.

  • C

    Reject the null; the genes are linked.

  • D

    The chi-square calculation is invalid.

Explanation

Chi-square (0.89) is below critical (3.84), so observed and expected do not differ significantly - data are consistent with the expected 3:1 monohybrid ratio.

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