Purebreed lines of fruit flies with wild type (tan) body color and stubbly brist

Question

Purebreed lines of fruit flies with wild type (tan) body color and stubbly bristles are mated to flies with ebony bodies and normal bristles. The resulting F1 offspring all have normal wild-type body color and stubbly bristles. The F1 flies are crossed with flies recessive for both traits (i.e. ebony bodies and normal bristles).

Assume you found the following results amount offspring:

Wild,stubby bristles 424

ebony, stubby bristles 58

wild type body,normal bristles 62

ebony body,normal bristles 456

How would you explain these results? Support with Chi square analysis.

(Note, normally the mating of CcBb x ccbb would results in a 1:1:1:1 phenotype ratio, I need to explain why it is like this instead please!!!!!!!!!)

Explanation / Answer

Step 1; Establish hypothesis : hypothesis is establish that 1:1:1:1 ratio will be found.

Step 2: Calculate the expected value of each set.: 424+58+62+456=1000

So, expected value in each case will be 1000/4= 250 (for getting the above ratio)

Step 3: Calculate chi square statistic

Chi square= sum of {(observed-expected)^2} / expected

                 = {(424-250) 2 / 250} + {(58-250) 2 / 250}+{(62-250) 2 / 250}+{(456-250) 2 / 250}

                  = 121.104 + 147.456 + 141.376 + 169.744

                   =579.68

So, the hypothesis is rejected using 3 degree of freedom, value chi square probability distribution table

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