23, 24, 25 Dihybrid crosses (23 & 24 are Guinea Pigs, 25 is Hair&Eye Color)

If you need a clearer picture of the handout, try here

So Mendel looked at his plants and wondered if the traits were related to each other, or if they were completely independent...  So he tracked plants that were hybrids of two traits (say Tt for tall/short and Yy for yellow/green seeds).

If the traits are truly independent, then whether or not you get a Y or a y has nothing to do with getting a T or t...(it's independent)

So a TtYy parent could produce:
TY
Ty
tY
ty
in equal ratios.  He then crossed the TtYy with a TtYy and made a really big Punnett square with two hybrids (A DIHYBRID CROSS!)
and found you could get
TTYY, TtYY, ttYY, TTYy, TtYy, ttYy, TTyy, Ttyy and ttyy in the expected phenotypic ratios of 9:3:3:1 of TALLYELLOW, TALLgreen, shortYELLOW, shortgreen.

Now you'll need to practice this a bit with the guinea pigs worksheet...

Check the links below for genetics tutorials, or find your own on youtube (search for dihybrid cross tutorial)