Question

Two autosomal genes control horn color in dragons. Pure-breeding gold-horned dragons were mated to pure-breeding silver-horned dragons. All of the F1 were gold. The F1 were intermated and the F2 generation consisted of 147 gold, 16 silver and 93 bronze.

Conduct a chi-square test to test the appropriate type of epistasis.
In the chi-square test, what is the expected number of gold-horned dragons? Round to two decimal places.

Conduct a chi-square test to test the appropriate type of epistasis.
In the chi-square test, what is the expected number of silver-horned dragons? Round to two decimal places.

Answer 1

Answer:

As per the information:

• Pure breeding gold-horned dragons x Pure breeding silver-horned dragons
• Let gold-horned dragon allele be represented by G
• Silver-horned dragon allele be represented by g
• GG x gg = Gg - All F1 generation were gold
• F1 generation was intermated: Gg x Gg

Punnett square for this cross can be represented as:

	G	g
G	GG	Gg
g	Gg	gg

F2 generation consists of 147 gold, 16 silver and 93 bronze (Total = 147 + 16 + 93 = 256)

Dominant epistatsis is suggested by 12:3:1 ratio

Recessive epistatsis is suggested by 9:3:4 ratio.

In this case the ratio is 9:6:1 which is similar to 9:4:3, indicating that epistasis is probably occurring between these two genes.

• Expected number of gold-horned dragons in epistatsis = 256*9/16 = 144
• Expected number of silver-horned dragons in epistasis = 256*1/16 = 16
• Expected number of bronze-horned dragons in epistatsis = 256*4/16 = 96

Chi square analysis can be performed as below:

Degree of freedom = Number of categories - 1 = 3 - 1 = 2

	Observed Frequency (O)	Expected Frequency €	(O-E)	(O-E)^2/E
GG	147	144	3	0.06
Gg	93	96	-3	0.09
gg	16	16	0	0.00
Total	256	256	Chi square (Sum)	0.16

P-value corresponding to chi square value of 0.16 with 2 degree of freedom: P-Value is 0.923116. The result is not significant at p < 0.05. There is sufficient evidence that there is no significant difference in observed frequency as compared to expected frequency based on the epistasis ratio of 9:6:1