Chapter 12, Problem 3ITD

Half of the world’s population eats rice at least twice a day. Much of this rice is grown in flooded conditions, and different strains of rice are tolerant (survive) or intolerant (die) under these conditions. Rice breeders used genetic crosses to test whether tolerance to flooding is a dominant trait. Researchers used three true-breeding flood-tolerant strains, FR143, BKNFR, and Kurk, and two true-breeding flood- intolerant strains, IR42 and NB, in the crosses. Results were obtained from three sets of crosses and are reported in the Table below:

Results of cross of F₁ to tolerant parent: F₁ plants were crossed with the tolerant parent of the cross.

	Number of Plants
Progeny Analyzed from Intolerant × Tolerant Cross	Alive	Dead	Total
1. F2 results of cross:
IR42 × FR13A	187	77	264
IR42 × BKNFR	192	73	265
NB × Kurk	142	52	195
2. Results of cross of F1 to intolerant parent:
(F1 of IR42 × FR13A) × IR42	14	17	31
(F1 of IR42 × BKNFR) × IR42	15	10	25
(F1 of NB × Kurk) × NB	21	35	56
3. Results of cross of F1 to tolerant parent:
(F1 of IR42 × FR13A) × FR13A	31	0	31
(F1 of IR42 × BKNFR) × BKNFR	28	0	28
(F1 of NB × Kurk) × Kurk	40	0	40

Do the data support the hypothesis that the tolerance trait is dominant? Justify your conclusion by explaining the results from each of the three sets of crosses in terms of genotypes and phenotypic ratios.

Source: T. Setter et al. 1997. Physiology and genetics of submergence tolerance in rice. Annals of Botany 79:67–77.