| Use these steps when determining the Genotypes and Phenotype that result from the crossing of two heterozygous Tall and Green Pea plants. |
| 1 | Assign a letter to represent each allele: |
| T = Tall Plant, t = Dwarf Plant, G = Green Pod Color, g = Yellow Pod Color | |
| 2 | Determine the Genotype of each parent and indicate the cross. |
| TtGg = heterozygous for Tall and Green T1t1 G1g1 x T2t2 G2g2 | |
| 3 | Determine all of the possible gametes that can be produced. Since they are both heterozygous, the results should be the same. |
| (T1G1, T1g1, t1G1, t1g1). | |
| 4 | Draw a four by four Punnett square. |
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| 5 | Place the alleles from one parent above the four squares and the other parent's alleles on the left side. |
| T1 G1 |
T1 g1 |
t1 G1 |
t1 g1 |
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| T2 G2 |
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| T2 g2 |
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| t2 G2 |
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| t2 g2 |
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| 6 | Determine all of the possible gametes these two parents can produce together and systematically, as in the mono-hybrid example, place them in the appropriate boxes. Your completed Punnett Square should look like this. |
| T1 G1 |
T1 g1 |
t1 G1 |
t1 g1 |
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| T2 G2 |
T1 T2 G1 G2 |
T1 T2 G2 g1 |
T2 t1 G1 G2 |
T2 t1 G2 g1 |
| T2 g2 |
T1 T2 G1 g2 |
T1 T2 g1 g2 |
T2 t1 G1 g2 |
T2 t1 g1 g2 |
| t2 G2 |
T1 t2 G1 G2 |
T1 t2 G2 g1 |
t1 t2 G1 G2 |
t1 t2 G2 g1 |
| t2 g2 |
T1 t2 G1 g2 |
T1 t2 g1 g2 |
t1 t2 G1 g2 |
t1 t2 g1 g2 |
| 7 | List the possible Phenotypes using the parents gametes as a guide. As you list a Phenotype, draw a diagonal from upper left to lower right through the cell. The results of drawing the diagonals should look like this. | |
| See the results in an Adobe Acrobat file (11K).
NOTE: This requires Adobe Acrobat Reader. |
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| Phenotype | Numbers |
| Tall and Green | 9 |
| Tall and Yellow | 3 |
| Dwarf and Green | 3 |
| Dwarf and Yellow | 1 |
| 8 | List all of the possible Genotypes. This is a little more time consuming as you may perceive the process to be random. Do it systematically by starting with the top left box (TTGG), describe and list the Genotype, and draw a diagonal through the box from the opposite direction (upper right to lower left) as you encounter the Genotype. It should not be difficult. | See the results in an Adobe Acrobat file (11K).
NOTE: This requires Adobe Acrobat Reader. |
| homozygous dominant/homozygous dominant | (T1T2G1G2) = 1 |
| homozygous dominant/heterozygous | (T1T2G2g1) = 2 |
| heterozygous/homozygous dominant | (T2t1G1G2) = 2 |
| heterozygous/heterozygous | (T2t1G1g2) = 4 |
| homozygous dominant/homozygous recessive | (T1t2g1g2) = 1 |
| heterozygous/homozygous recessive | (T1t2g1g2) = 2 |
| homozygous recessive/homozygous dominant | (t1t2G1G2) = 1 |
| homozygous recessive/heterozygous | (t1t2G1g2) = 2 |
| homozygous recessive/homozygous recessive | (t1t2g1g2) = 1 |
