One way to analyse multiallelic TDT results is to look at each allele in turn to see if the number of times it is transmitted from heterozyogous parents differs significantly from the number of times it is not transmitted:
Transmissions for individual alleles:
1 2 3 4
Passed: 28 19 25 10
Not passed: 10 33 24 15
Chi-squared: 8.526 3.769 0.020 1.000
p values: 0.0035 0.0522 0.8864 0.3173
(these p values should be corrected for multiple testing)
Each chi-squared statistic is calculated according to SUM(O-E)2/E, where the expected number of times for the allele to be passed and not passed is half the total number of times a heterozyogous parent has the allele. E.g. for allele 1, chi-squared = (28-19)2/19+(10-19)2/19
This chi-squared statistic has one degree of freedom, but since one may be testing multiple alleles in turn, the p value must be corrected.