The number of degrees of freedom for a test cross of an ss/rr individual would be

To determine the number of degrees of freedom (df) for a test cross of a ss/rr individual, one first needs to understand the genotype being described and the type of genetic cross being performed.

An ss/rr individual is homozygous recessive for both of its traits, 's' and 'r'. In a test cross, this individual will be crossed with another individual that is heterozygous for both traits (SsRr), which is commonly used to determine the genotype of an individual showing the dominant phenotype for both traits.

The progeny from such a test cross can have four possible phenotypic combinations, corresponding to the four possible gametes that the SsRr individual can produce: SR, Sr, sR, and sr. The four resulting phenotypes would be SsRr (showing both dominant traits), Ssrr (showing the dominant phenotype for 'S' but recessive for 'r'), ssRr (showing the recessive phenotype for 's' but dominant for 'r'), and ssrr (showing recessive phenotypes for both).

When you perform a chi-square test to analyze the data from this test cross, the number of degrees of freedom is one less than the number of possible phenotypic categories. Since there are four potential phenotypes, the degrees of freedom would be:

df = number of categories - 1 df = 4 - 1 df = 3

So, the number of degrees of freedom for a test cross of an ss/rr individual would be 3.