Question

Corn #1 is a standard F2 generation of a monohybrid cross. The trait you will be following here is the endosperm characteristic making the corn either starchy or sweet. The information in red was obtained by in the lab by counting how many are displaying each of the following phenotypes

Number starchy(smooth) 232 Number sweet(wrinkled) 72

What is the expected ratio? Perform a chi square below. Determine your probability value ______ and analyze what that means.  

Answer 1

Representation: Monohybrid cross

Starchy (smooth): Dominant trait

Homozygous genotybe = SS

Heterozygous genotybe =Ss

Sweet (wrinkled): Recessive trait

Homozygous genotybe = ss

Cross: True breeding

SS xss

	s	s
S	Ss	Ss
S	Ss	Ss

F1: All are Ss = Starchy

Ss x Ss

	S	s
S	SS	Ss
S	Ss	ss

F2:

Starchy = SS/Ss = 3/4

Sweet = ss = 1/4

Ratio =3:1

Chi square test:

Phenotype	O	E	O-E =d	d2	Χ2 (d2/E)
Starchy	232	3/4 x 304= 228	(232 – 228) = 4	16	16/228 = 0.07
Sweet	72	1/4 x 304 = 76	(72-76) = -4	16	16/76 = 0.21
Total	304				0.28

· Here only one trait is considered, df =1.

· Critical value for df= 1, p= 3.84

· Since Χ2 value in this case 0.28.

· Thus, hypothesis is accepted.