5.1 – 5.2 Problem Solving
1. Mendel crossed true breeding plants that produced round seeds (RR) with true breeding
plants that produced wrinkled weeds (rr). Use a Punnett squares to find genotypes and
phenotypes of the F1 and F2 generations. Predict the ratio of F2 plants with round seeds to
F2 plants with wrinkled seeds.
2. Black fur is dominant (B) and white fur is recessive (b) in guinea pigs. A black guinea
pig with unknown genotype is mated with a white guinea pig. Outline a procedure that
could be used to determine if the black guinea pig is pure bred for hair colour. Include
Punnett squares to illustrate your conclusions.
3. Why can you calculate the probability of a phenotype by adding the probabilities of all
genotypes that produce that phenotype?
4. Mendel took true breeding pea plants that had purple flowers and were tall (PPTT) and
crossed them with true breeding pea plants that had white flowers and were short (pptt).
a) Fill in the blanks to determine the genotype and phenotype of the F1 generation of plants.
P phenotypes: purple flowers
X
P genotypes:
X
P gametes:
PT, PT, PT, PT
F1 genotypes:
X
short plants
pt, pt, pt, pt
all are PpTt
F1 phenotypes:
all
flowers and
plants
b) Fill in the blanks to determine the genotypes of the F2 generation by completing the
Punnett square.
♂ & ♀
PT
Pt
pT
pt
PT
Pt
pT
pt
F2 Ratio of phenotypes:
5. In maize, coloured seeds are dominant (A) and colourless seeds are recessive (a). Normal
starch is a dominant trait (W) and waxy starch is a recessive trait (w). To determine the
genotype of a plant with coloured seeds and normal starch, you perform a test cross. The
resulting ear of corn has 350 coloured seeds with normal starch and 335 colourless seeds
with normal starch. What is the genotype of the parent plant with coloured seeds and
normal starch?