WLHS / BIOLOGY / MONSON / UNIT 6 - GENETICS
Name
Date Per.
Genetics Problem Set #2 - Monohybrid and Dihybrid Crosses
Punnett Square Example: In pea plants, tall (T) is dominant over short (t). Cross a pure tall plant with a pure
short plant. Find the genotype and phenotype ratios.
CROSS: TT x tt
genotype ratio: all hybrid (heterozygous)
phenotype ration: all tall
Simple Probability & Monohybrid Crosses:
1) The Jones family has eight children, all of whom are girls. What is the chance that the next child will be a
boy? Explain.
2) In pea plants, round seed shape (R) is dominant over wrinkled (r). Write the genotype and phenotype for a plant
that is:
a) heterozygous (hybrid):
b) homozygous dominant (pure):
c) homozygous recessive (pure):
3) Find the genotype and phenotype ratios expected from crossing two heterozygous
plants from problem #2.
4) In a certain plant, yellow fruit (Y) is dominant to white fruit (y). A heterozygous plant with yellow fruit is crossed
with a plant with white fruit. Find the genotype and phenotype ratios.
5) In horses, black color (B) is dominant over chestnut color (b). Find the genot ype and phenotype ratios of a cross
between a hybrid black horse and a chestnut horse. What is the probability that the offspring will be chestnut
color?
6) In humans, normal pigmentation is due to a dominant factor "C," albinism to its recessive allele "c." A normal
man marries an albino woman. Their first child is an albino.
(a) What are the genotypes of these three people?
man: woman: child:
(b) If they have more children, what would they probably be like? (i.e. what % will be “normal” vs. albino?)
T
T
t
Tt Tt
t
Tt Tt
