Strategy to make triple mutant and multiple mutants.
If you need to calculate progeny segregation, a the Punnett Sqare calculator can be found at: http://scienceprimer.com/punnett-square-calculator
Planning of crosses to generate double/triple/quadruple/… mutant can save a lot of time. When generating a triple mutant, lets say the aabbcc mutant the bad strategy (although commonly used one) is to cross aabb with cc, in doing so the F2 has to be screened at all three loci. However if aabbCC was crossed with aaBBcc then only b and c would have to be screen. Here is the demonstration of how much work can be saved.
To get the triple:
Wrong way to do it (your ab mutant X c mutant)
aabbCC X AABBcc
F1: all individuals are heterozygous again AaBbCc
F2: 1/64 plant are aabbcc
As a result a minimum of 64 plants should be screened.
Correct way to proceed.
Generate all possible combination for you doubles.
Cross aabbCC with aaBBcc. In this case you don’t have to screen for aa
F1: all individuals are homo for aa and heterozygous BbCc
F2: 1/16 plant are aabbcc
Only 16 plants have to be screened