Question

PART A) The color of tulips can be determined by the interaction of 2 loci. Tulips can be pigmented red (controlled by a dominant allele, R) or yellow (r). The second locus has a dominant white allele (W), which inhibits pigment resulting in white tulips and a recessive allele (w) which results in colored petals. Consider the cross of a true breeding yellow tulip with a true breeding white tulip that is heterozygous recessive at the pigmented locus. Show work where necessary. What are the parental genotypes? What are the resulting F1 genotypes? If you cross the F1 plants what is the probability of getting a white tulip in the F2 generation?

PART B) A true-breeding pink-body unicorn with a red horn was crossed with a true-breeding white-bodied, purple horned unicorn. Pink body and purple horns are dominant. What phenotypic ratio do you expect for F1? For the F2 generation, you end up with the following unicorn offspring: 180 pink-bodied and purple horned, 60 pink-bodied and red horned, 50 white-bodied and purple horned, and 15 white bodied and red horned. Test the hypothesis that the genes associated with unicorn body and horn color are assorting independently. What is your chi-square value?  Now assume that your chi-square value exceeds the chi-square critical value. Does this mean you reject or fail to reject your null hypothesis.  Now assume that you failed to reject your null hypothesis, does this mean the two genes are independently assorting or that linkage is occurring?

Answer 1

Answer:

Part A).

Yellow (rrww) x RrWW (white) ---Parents

F1

	RW	rW
rw	RrWw (white)	rrWw (white)

RrWw x rrWw ---F1 intercross

	rW	rw
RW	RrWW (white)	RrWw (white)
Rw	RrWw (white)	Rrww (red)
rW	rrWW (white)	rrWw (white)
rw	rrWw (white)	rrww (yellow)

Red (1) : White (6) : yellow (1)

Part B).

Pink-bodied, red horn (PPrr) x (ppRR) white-bodied, purple horn –Parents

PpRr (pink-bodied, purple horn)----------------------F1

PpRr x PpRr –F1 selfcross

F2:

	PR	Pr	pR	pr
PR	PPRR (pink, purple)	PPRr (pink, purple)	PpRR (pink, purple)	PpRr (pink, purple)
Pr	PPRr (pink, purple)	PPrr (pink, red)	PpRr (pink, purple)	Pprr (pink, red)
pR	PpRR (pink, purple)	PpRr (pink, purple)	ppRR (white, purple)	ppRr (white, purple)
Pr	PpRr (pink, purple)	Pprr (pink, red)	ppRr (white, purple)	pprr (white, red)

Expected values:

Total progeny = 180+60+50+15 = 305

Pink, purple = 9/16 * 305 = 171.56

Pink, red = 3/16 * 305 = 57.19

White, purple = 3/16 * 305 = 57.19

White, red = 1/16 * 305 = 19.06

Phenotypes	Observed(O)	Expected (E)	O-E	(O-E)2	(O-E)2/E
pink, purple	180	171.56	8.44	71.19	0.415
pink, red	60	57.19	2.81	7.91	0.138
white, purple	50	57.19	-7.19	51.66	0.903
white, red	15	19.06	-4.06	16.50	0.866
Total	305	305			2.322

Chi-square value = 2.322

Degrees of freedom = 4-1=3

p-value = 7.814

The Chi-square value (2.322) is less than critical (p) value (7.81). So the given data is consistant with expected results. So we can accept null hypothesis and the genes are assorted independently.