J. A. Moore investigated the inheritance of spotting patterns in leopard frogs. The pipiens phenotype had the normal spots that give leopard frogs their name. In contrast, the burnsi phenotype lacked spots on its back. Moore carried out the crosses in the table, producing the progeny indicated. (Moore, 1943).
Cross Parent phenotypes Progeny phenotypes, observed
1 burnsi x burnsi 39 burnsi, 6 pipiens
2 burnsi x pipiens 23 burnsi, 33 pipiens
3 burnsi x pipiens 196 burnsi, 210 pipiens
Calculate the expected numbers of progeny.
Identify the expected phenotypic ratios for the progeny of the burnsi x burnsi cross. Define the burnsi allele as B and the pipiens allele as B+.
a. 2 burnsi : 1 pipiens.
b. 1 burnsi : 1 pipiens.
c. 3 burnsi : 1 pipiens .
Before the chi‑square test can be used to evaluate the fit of the observed data, the expected numbers of progeny need to be determined. In this burnsi × burnsi cross, how many progeny would be expected for the burnsi phenotype, assuming there are 45 total progeny? In this burnsi × burnsi cross, how many progeny would be expected for the pipiens phenotype, assuming there are 45 total progeny? pipiens progeny:

Expected number of the progeny: We know that the total number of individuals in the F1 is 45, which is 100% of the progeny. We need to calculate what are the expected numbers according to the expected proportions. So,

100% of the progeny---------45 individuals

25% B B -------------------------X = (25 x 45)/100 = 11.25 individuals B B

50% B B+------------------------X = (50 x 45)/100 = 22.5 individuals B B+

25% B+ B+ ----------------------X = 11.25 individuals B+ B+

33.75 individuals are expected to be burnsi, and 11.25 individuals are expected to be pipiens.

Cross 2: burnsi x pipiens

Parental) B B+ x B+ B+

F1) Expected genotype: 50% =2/4 B+ B, 50% = 2/4 B+ B+

Expected phenotype: 50% = 2/4 burnsi and 50% = 2/4 pipiens

Expected number of the progeny: We know that the total number of individuals in the F1 is 56, which is 100% of the progeny. We need to calculate what are the expected numbers according to the expected proportions. So,

100% of the progeny---------56 individual

50% B B+------------------------X = (50 x 56)/100 = 28 individuals B B+

50% B+ B+ ----------------------X = 28 individuals B+ B+

28 individuals are expected to be burnsi, and 28 individuals are expected to be pipiens.

Cross 3: burnsi x pipiens

Parental) B B+ x B+ B+

F1) Expected genotype: 50% =2/4 B+ B, 50% = 2/4 B+ B+

Expected phenotype: 50% = 2/4 burnsi and 50% = 2/4 pipiens

Expected number of the progeny: We know that the total number of individuals in the F1 is 406, which is 100% of the progeny. We need to calculate what are the expected numbers according to the expected proportions. So,

100% of the progeny---------406 individual

50% B B+------------------------X = (50 x 406)/100 = 203 individuals B B+

50% B+ B+ ----------------------X = 203 individuals B+ B+

203 individuals are expected to be burnsi, and 203 individuals are expected to be pipiens.

The expected phenotypic ratios for the progeny of the burnsi x burnsi cross

The correct answer is option c. 3 burnsi : 1 pipiens. Both parentals are heterozygous, which means that the F1 ratio is expected to be 3:1, (1/4 B B and 2/4 B B+) : (1/4 B+ B+)

Expected burnsi phenotype progeny from the burnsi × burnsi cross, where N= 45

Expected burnsi phenotype: 75% = 3/4 burnsi and 25% = 1/4 pipiens