MONOHYBRID PUNNETT SQUARE PRACTICE
Background:
A Punnett Square is a visual tool used by scientists to determine the possible combinations of
genetic alleles in a cross. Since genes are inherited randomly and independently, Punnett Squares
are useful for looking at just one gene combination (monohybrid) or a whole series of combinations
(dihybrid for two traits, etc.)
To make a Punnett Square, draw a box and then divide it into four smaller squares. On the top of
the box write the letters that correspond with the alleles for one parent. Write the alleles for the
other parent along the left side of the box. Use an upper case letter for a dominant allele and a
lower case letter for a recessive allele. Fill in the smaller squares with the alleles from the
corresponding rows and columns. The resulting alleles combinations are the possible genotypes for
the offspring from that cross.
Example:
A green pea plant (GG) is being crossed with a green pea plant (Gg).
Activity:
Use the provided Punnett Squares to determine the genotypes and phenotypes of each cross.
1. A green pea plant (Gg) is crossed with a yellow pea plant (gg).
2. A tall plant (TT) is crossed with a tall plant (Tt).
3. A tall plant (Tt) is crossed with a short plant (tt).
4. A red flower (Rr) is crossed with a white flower (rr).
G
G
G
GG
GG
g
Gg
Gg
Genotypes: 50% GG, 50% Gg
Phenotypes: 100% green
