Q: In a dominant epistasis cross with a 12:3:1 ratio, if you observe 714 white, 174 yellow, and 72 green offspring, what is the expected number of yellow offspring out of 960 total?

$$E_{yellow} = \frac{3}{16} \times 960 = 180$$

Q: In a duplicate recessive epistasis cross (9:7 ratio), if you observe 306 white and 258 purple offspring, what is the expected number of purple offspring out of 564 total?

$$E_{purple} = \frac{7}{16} \times 564 = 246.75$$

Question 1

Which formula is used to calculate the Chi-Square ($$\$$chi^2$$) statistic in genetics for goodness-of-fit tests?

Accepted Answer

$$\$$chi^2$$ = \sum \frac{(O - E)^2$}{E}$$

Question 2

In a dominant epistasis cross with a 12:3:1 ratio, if you observe 714 white, 174 yellow, and 72 green offspring, what is the expected number of yellow offspring out of 960 total?

Accepted Answer

$$E_{yellow} = \frac{3}{16} 	imes 960 = 180$$

Question 3

What is the degrees of freedom ($$df) $$for a chi-square test involving three phenotypic classes?

Accepted Answer

$$df = 3 - 1 = 2$$

Question 4

If the calculated $$\$$chi^2$$ value is 0.559 and the critical value at p=0.05$ and df=2$ is 5.99, what is the correct interpretation?

Accepted Answer

Fail to reject the null hypothesis; observed data fits expected ratio.

Question 5

In a duplicate recessive epistasis cross (9:7 ratio), if you observe 306 white and 258 purple offspring, what is the expected number of purple offspring out of 564 total?

Accepted Answer

$$E_{purple} = \frac{7}{16} 	imes 564 = 246.75$$

Question 6

Which of the following is a plausible reason for failing to reject the null hypothesis in a chi-square test?

Accepted Answer

The calculated $$\$$chi^2$$ value is less than the critical value.

Question 7

Given the formula $$\$$chi^2$$ = \sum \frac{(O - E)^2$}{E}$$, what does $$O$$ represent?

Accepted Answer

Observed value

Question 8

If you have a cross with a 9:7 ratio and observe 306 white and 258 purple offspring, what is the $$\$$chi^2$$ value for the purple class?

Accepted Answer

$$\$$chi^2$$_{purple} = \frac{(258 - 246.75)^2$}{246.75} = 0.511$$

Question 9

Which interaction type has a critical value of 3.84 for $$df=1 at$$ $$p=0.05$$ according to the summary table?

Accepted Answer

Duplicate Recessive

Question 10

A student performs a chi-square test and gets $$\$$chi^2$$ = 0.2254$$ with $$df=1. $$The critical value is 3.84. What should the student conclude?

Accepted Answer

Fail to reject the null hypothesis; the observed data fits the expected ratio.

Question 11

Which of the following ratios is associated with dominant epistasis?

Accepted Answer

12:3:1

Question 12

If the expected values in a chi-square test are 720, 180, and 60, and the observed values are 714, 174, and 72, what is the $$\$$chi^2$$ value for the green class?

Accepted Answer

$$\$$chi^2$$_{green} = \frac{(72 - 60)^2$}{60} = 2.4$$

Question 13

What is the purpose of the chi-square test in genetics?

Accepted Answer

To determine if observed offspring counts fit expected genetic ratios.

Question 14

Which of the following is NOT a step in performing a chi-square test?

Accepted Answer

Calculating the mean of observed values.

Question 15

In a genetic cross, the observed values are very close to the expected values. What would you expect the $$\$$chi^2$$ value to be?

Accepted Answer

Low

Question 16

If the null hypothesis is rejected in a chi-square test, what does this imply about the genetic cross?

Accepted Answer

The observed data does not fit the expected Mendelian ratio.

Question 17

Which ratio is associated with duplicate dominant epistasis?

Accepted Answer

15:1

Question 18

What is the critical value for $$df=2 at$$ $$p=0.05$$ according to the summary table?

Accepted Answer

5.99

Question 19

A researcher observes a 9:3:4 ratio in a genetic cross. What type of epistasis is most likely occurring?

Accepted Answer

Recessive epistasis

Genetics Chi-Square Test: Epistasis and Hypothesis Testing

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