1. 6 Basic Steps to Completing Single Cross Punnett Squares
Problem : A harmless chemical known as PTC can be
added to strips of paper to test for the presence of
dominant & recessive alleles. Being able to taste the
chemical (T) is dominant to being a non-taster (t).
If two heterozygous tasters are crossed, what are the
possible genotypes and phenotypes of their children?
Step #1 – Create a key showing traits as
dominant/recessive.
T = PTC taster
t = non-taster

2. 6 Basic Steps to Completing Single Cross Punnett Squares
Step # 2 – Make a list of possible allele combinations & the phenotypes that each would produce. TT= PTC-taster Tt = PTC-taster tt = non-taster Step # 3 – Identify the parents that are being used in the cross. Tt x Tt

3. 6 Basic Steps to Completing Single Cross Punnett Squares
Step # 4 – Draw a Punnett square to determine possible offspring.
T t
T TT Tt
t Tt tt
Step # 5 – Identify the Genotypic ratio.
1 : : 1
TT Tt tt
Step # 6 – Identify the Phenotypic ratio. :
PTC-tasters non-taster