Question

J.A. Moore investigated how spotting patterns were inherited in leopard frogs (Moore, 1943). There are two phenotypes. The pipiens phenotype had the normal spots that give the leopard frogs their name, whereas the burnsi phenotype has no spots on its back. Moore carried out the following experimental crosses, producing the progeny indicated Parent phenotypes Offspring phenotypes burnsi x burnsi 39 burnsi, 6 pipiens burnsi x pipiens 23 burnsi, 33 pipiens burnsi x pipiens 196 burnsi, 210 pipiens a) On the basis of these results, what is the most likely mode of inheritance for the burnsi phenotype (i.e. is it dominant or recessive)? b) Give the most likely genotypes of the parent in each cross (define the symbols you decide to use for each allele) c) Use a chi-square test to evaluate whether the observed number of progeny fit to the number expected from your proposed genotypes.

Answer 1

a) In this example, burnsi phenotype is dominant while pipiense phenotype is recessive.

b) If the gene spotting patterns is A, than allele A is dominant over allele a.The genotypes of the parents from the first cross are Aa x Aa, the second cross: Aa x aa and from the third: Aa x aa

c) A chi-square test compares observed with expected data and the formula is:

X2 =∑ (observed value-expected value)2/(expected value)

P: Aa x Aa

F1: AA Aa Aa aa ratio is 3:1

This means that in the whole number of animals 39+6=45, expected values would be : 45/4=11.25, expected value for the burnsi phenotype is 11.25*3=33.75, and for the pipins is 11.25

So, x2= ((39-33.75)2/33.75) + ((6-11.25)2/11.25) = 0.82+2.45=3.27

The same thing with other two crosses.