Chi-square analysis of crosses Transitional Reasoning Practice

Questions

1. 1.

   In a study on mouse coat color inheritance, a cross between double heterozygotes yields 160 progeny consisting of 84 agouti, 36 black, and 40 albino individuals. A geneticist hypothesizes that these genes exhibit recessive epistasis, which predicts a 9:3:4 phenotypic ratio. Given that the critical chi-square value at $p = 0.05$ is 5.99 for 2 degrees of freedom and 7.81 for 3 degrees of freedom, which evaluation correctly interprets this goodness-of-fit test?

   • A) The calculated $\chi^2$ value is 4.80, which exceeds the threshold at 2 degrees of freedom, so the recessive epistasis model is rejected.
   • B) The calculated $\chi^2$ value is 1.60, which is less than the critical value of 5.99 for 2 degrees of freedom, supporting the recessive epistasis hypothesis.
   • C) The calculated $\chi^2$ value is 1.60, but because there are three phenotypic classes the test has 3 degrees of freedom, leading to an incorrect rejection of the model.
   • D) The calculated $\chi^2$ value is 6.40, which exceeds the critical value of 5.99 for 2 degrees of freedom, indicating that the genes sort independently without epistasis.

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