Use the Phenotypic Ratio Calculator to work with phenotype counts/frequencies. In the Basic tab, enter the frequency (or count) of the first phenotype class (F1) and the least-frequent phenotype class (FS) to compute the first-to-smallest ratio factor (F1/FS). For multi-class phenotypic ratios (e.g., 9:3:3:1), use the Ratio Tools tab, and for goodness-of-fit testing use the Chi-Square Test tab.

Phenotypic Ratio Calculator

Basic
Ratio Tools
Chi-Square Test

Enter any 2 values to calculate the missing variable

Phenotypic Ratio Formula

A phenotypic ratio in genetics is normally written as a colon-separated ratio across phenotype classes (e.g., 3:1, 9:3:3:1). The calculator also supports a two-class normalization in the Basic tab, reporting the first-to-smallest ratio factor.

\text{Phenotypic ratio} = F_1 : F_2 : \dots : F_n
R_{1:S} = \frac{F_1}{F_S}
  • Where F1, F2, …, Fn are the phenotype counts/frequencies for each phenotype class (the ratio is written as F1:F2:…:Fn and then simplified).
  • FS is the smallest (least-frequent) phenotype count/frequency among the classes (used for the Basic-tab normalization).
  • R1:S is the first-to-smallest ratio factor (dimensionless), equal to F1/FS.

To report a phenotypic ratio from observed data with multiple phenotype classes, write the counts/frequencies as F1:F2:…:Fn and simplify (often by dividing by the greatest common divisor). For the two-class case, dividing F1 by FS gives the first-to-smallest factor; you can also express the ratio as F1:FS and simplify.

How to Calculate Phenotypic Ratio?

The following example problems outline how to calculate a two-class normalized phenotypic ratio (Basic tab).

Example Problem #1:

  1. First, determine the frequency (or count) of the first phenotype class.
    • The frequency of the first phenotype is given as: 15.
  2. Next, determine the frequency (or count) of the least-frequent phenotype class (the smallest count).
    • The frequency of the least-frequent phenotype is provided as: 5.
  3. Finally, calculate the first-to-smallest ratio factor using the equation above.

R1:S = F1 / FS

The values given above are inserted into the equation below and the solution is calculated:

R1:S = 15 / 5 = 3, which corresponds to a simplified two-class ratio of 15:5 = 3:1.

Example Problem #2: 

For this problem, the variables required are provided below:

frequency of the first phenotype = 16

frequency of the least-frequent phenotype = 6

Test your knowledge using the equation and check your answer with the calculator above. (Tip: 16:6 simplifies to 8:3, and the Basic tab’s factor is 16/6 ≈ 2.6667.)

R1:S = F1 / FS = ?