Punnett Square Method
Follow my steps to carry out a Punnett square problem...(unfortunately the steps are shown in detail in class. These notes will make more sense if you weren't absent. If you were, set up a time after school to learn it!)

Problem: A homozygous tall pea plant is crossed with a short pea plant. (Remember, tall is dominant over short for pea plants!) What would the expected genotypes (the genotypic ratio) and phenotypes (the phenotypic ratio) of their offspring?

STEP 1: set up the key that will show how each allele (form of a gene) will be shown

T = tall
t = short

STEP 2: set up the parents that will be crossed; use the information from the word problem itself

TT x tt
a tall homozygous parent a short parent

remember, to be short, it has to have both short alleles!

STEP 3: do the Punnett square; that is, put one parent on the top and the other parent on the left of the square...then from a blank box, take the allele on the top and the allele from the left and fill them in

STEP 4: show the results (ratios) of the cross

GENOTYPIC RATIO:

PHENOTYPIC RATIO:

TRY THESE PUNNETT SQUARE PROBLEMS
1) Use a Punnett square to show the offspring of a cross between two pea plants that are heterozygous for height (Tt). Give the phenotype and genotypes of the offspring. (That is, what is the phenotypic and genotypic ratios!)

2) Use a Punnett square to show the offspring of a cross between a pea plant that is homozygous tall and one that is heterozygous. Give the phenotypes and genotypes of the offspring.

3) Use a Punnett square to show the offspring of a cross between a pea plant that is heterozygous tall and one that is homozygous recessive for height. Give the phenotypes and genotypes of the offspring.