This is a great one-day lesson on how Punnett Squares work. It is the first in a series of four lessons for middle school genetics. Students discover for themselves the ins and outs using dominant, recessive, homozygous, and heterozygous vocabulary words. It has some accommodations and modifications for kids with special needs. I have used it with much success over the years. For the entire week's unit, see my Genetics Week 1.