Question

Perform a chi-square test to determine if an observed ratio of 40 tall:10 dwarf pea plants is consistent with an expected ratio of 1:1 from the cross of Dd x dd.

What is your degrees of freedom

What is your critical value

Is this observed ratio consistent with an expected ratio of 1:1? (yes or no)

Answer 1

Null hypothesis: the alleles are segregated during the gamete formation so for the cross Dd* dd it follows the ratio 1;1

alternative hypothesis: data is not consistent with 1:1 ratio from the cross Dd*dd

observed ratio is tall : dwarf=40:10=4:1

phenotype	observed (O)	Expected (E)	(E-O)^2/E
tall	4	1	9
dwarf	1	1	0

chi-square value=9

degrees of freedom= number of phenotypes-1=2-1=1

for P <0.05

the critical value for df=1 and P<0.05 is 3.841

chi-square value is less than critical value so we reject null hypothesis.

observed ratio is not consistent with an expected ratio of 1:1.