Genetics Practice Problems – Q&A
Probability:
Q1. A die (singular of dice) has 6
sides. What is the probability that an
even number will come up on one
throw of a die?
Q2. The Jones family has 8 children,
all of whom are girls. What is the
chance that the next child will be a
boy? Explain.
Q3. What types of gametes would be produced by
an organism having the genotype AaBB for 2 traits?
(Hint – use arrows to determine all possibilities)
A1:
A2:
A3:
Traditional Mendelian Dominant/Recessive Inheritance:
Q1. Widow’s peak is dominant.
What are the possible
phenotypes of the offspring of a
man homozygous dominant
(WW) and a heterozygous
woman (Ww)? Show Punnett
square and answer.
Q2. In garden peas, tall vine
is dominant and short vine is
recessive. If a homozygous
tall plant is crossed with a
homozygous short plant,
what genotypes are possible
in the F1 generation? Show
Punnett square and answer.
Q3. Albinism is a recessive
disease causing lack of
pigment. What are the
chances of an albino man
and a carrier woman having
an albino child? Show
Punnett square and give
answer as a percentage.
Q4. Guinea pigs can have short
hair or long hair. A short-haired
male and a short-haired female
produced mostly short-haired
offspring, but a few were longhaired. Is short hair dominant or
recessive? Do a Punnett square
that explains the above.
A1.
A2.
A3.
A4.
Mendelian Problems using F1 and F2 generation:
Q1. In summer squash, white fruit color is dominant (W) and
yellow is recessive (w). A squash plant that is homozygous for
white (WW) is crossed with a homozygous yellow one (ww).
Do a Punnett square and predict the phenotypes of the F1 and
F2 generations. Remember you cross 2 F1’s to get the F2
generation.
A1.
Punnett Square
Phenotype Ratios
Q2. In garden peas, inflated pod is dominant and constricted
pod is recessive. A true-breeding inflated pod plant is crossed
with a true-breeding constricted pod plant.
Do a Punnett square and predict the phenotypes of the F1
and F2 generations. Remember you cross 2 F1’s to get the
F2 generation.
Lastly – if there are a total of 100 offspring in the F2
generation, how many of these will have constricted pods?
A2.
Punnett Square
Phenotype Ratios
F1
F1
F2
F2
How many out of 100 F2 offspring will have constricted
pods?_____________
Codominance
Multiple alleles
Q1. Snapdragon plants exhibit
incomplete dominance for flower color.
What percentage of plants will have red
flowers if you cross 2 pink-flowered
plants? Do the Punnett square and give
answer.
Incomplete Dominance
Q1. Coat color in cattle follows the
codominant pattern of inheritance with
possible phenotypes of red, white, or
roan (both red and white) hair. What are
the genotypes and phenotypes that result
from crossing a red cow (RR) with a
white bull(rr)?
Q1. Rabbit coat color has multiple
alleles with a hierarchy of dominance.
Grey (C) dominates over chinchilla (cch)
which dominates over Himalayan (ch)
which dominates over albino(c). What
phenotype will result from each of the
genotypes listed below?
A1.
A1.
A1. Cc =
CC =
cchc =
cc =
Cch =
ch c =
Blood Types (Codominance and Multiple Alleles) – can use A, B, O instead of I’s
Q1. What is the probability that a couple
whose blood types are AB and O will
have a type A child? Show Punnett
square and give answer in percentage.
Q2. A type A woman whose father was
type B marries a type B man whose
mother was type A. What will be their
children's possible genotypes and
phenotypes? Show Punnett square and
answers.
Q3. A couple has a child with type A
blood. If one parent is type O, what are
the possible genotypes of the other
parent?
Do a Punnett square, filling in
everything you know and a question
mark for what you don’t know.
A1.
A2.
A3.
X-linked (Sex-Linked) – use N for normal, n for hemophilia or color-blindness or white eyes
Q1. If a woman who is a carrier for
hemophilia marries a normal male, what
is the chance they will have a child with
hemophilia? What is the chance their
son will have hemophilia?
Do the Punnett square – remember your
X and Y chromosomes!! Don’t put
anything on the Y!!
Q2. If a normal-sighted woman whose
father was color-blind marries a colorblind man, what is the probability that
their son will be color-blind? What is
the probability that their daughter will be
color-blind?
Do the Punnett square – remember your
X and Y chromosomes!! Don’t put
anything on the Y!!
Q3. In fruit flies, white eyes is a sexlinked trait. Normal eye color is red. If
a white-eyed male is crossed with a
heterozygous female, what proportion of
the offspring will have red eyes?
Do the Punnett square – remember your
X and Y chromosomes!! Don’t put
anything on the Y!!
A1.
A2.
A3.
Pedigrees:
Label each pedigree with the type of inheritance it demonstrates:
Choose from Autosomal recessive, Sex-linked (X-linked), or Autosomal dominant
Type: _________________
Type_________________
Type___________________
PRACTICE IDENTIFYING TYPES OF INHERITANCE: (Use your guided notes to help)
Choose from the following types of inheritance and write in the box which one is described by each situation:
2 linked genes (little or no crossing over)
Polygenic (several to many genes)
Multiple alleles – hierarchy of dominance
Incomplete dominance
Dihybrid cross – 2 genes on different chromosomes
Type of Inheritance
Situation
1) In the F2 generation of a certain plant, ¼ have no thorns, ¼ have long thorns, and ½
have short thorns.
2) In another set of plants, also an F2 generation, you find the following phenotype ratios:
9 red flowers with broad leaves, 3 red flowers with narrow leaves, 3 white flowers with
broad leaves, and 1 white flower with narrow leaves.
3) In a certain species of bird, you see some birds with barely any crest on their head,
some with very long crests, and many birds with crests of all possible lengths in between.
4) In a certain species of insect, three eye colors are known: red, orange, and yellow. If
purebred red-eyed individuals are crossed with purebred orange-eyed, all the offspring are
red-eyed. If purebred orange-eyed are crossed with purebred yellow-eyed, all the
offspring are orange-eyed. If purebred red-eyed are crossed with purebred yellow-eyed,
all the offspring are red-eyed.
5) In another case in which you study 2 traits of a plant at the same time, you find in the
F2 generation that ¾ have hairy stems and green seeds while the other ¼ have smooth
stems and brown seeds.
Challenge: (How good are your genetic skills?!!) – do on separate paper
1) The polled (hornless) trait in cattle is dominant. The horned trait is recessive. A certain polled bull is mated to 3 cows. Cow
A, which is horned, gives birth to a polled calf. Cow B, also horned, produces a horned calf. Cow C, which is polled, produces a
horned calf. Name the genotypes of all parents.
2) In poultry, rose comb is a dominat trait (R), single comb is recessive (r). A rose combed male is mated with 2 rose combed
females. Female A produces 14 chicks, all rose-combed. Female B produces 9 chicks, 7 rose-combed and 2 single-combed.
What are the genotypes of the 3 parent birds?
3) In sheep, white coat is dominant to black. Occasionally, a black sheep appears in a flock. Black wool is worthless. How
could a farmer eliminate the genes for black coat from the flock?
4) Suppose you examined the cells of a species of plant and found 12 chromosomes: a long straight pair, a short straight pair, a
medium-length straight pair, a long bent pair, a short bent pair, and a medium-length bent pair. You then breed the plants of this
species for several generations. At the end of this time, would you expect to find some plants with all the straight chromosomes
and none of the bent ones? Or vice versa? Explain.
5) In snapdragons, red flower color (R) is incompletely dominant to white (r), the heterozygotes being pink. And the normal
broad leaves (B) are incompletely dominant to narrow leaves, the heterozygotes having leaves of medium breadth. If a redflowered, broad-leaved plant is crossed with a white-flowered, narrow-leaved one, what will be the phenotypes and their
expected ratios in the F2 generation?
6) In mice, black fur color is dominant to brown. A brown mouse is crossed with a heterozygous black mouse. If the mother has
a litter of four, what are the chances that all of them will be brown?
7) In dogs, wire hair is a dominant trait, smooth hair is recessive. Two wire-haired dogs produce a male puppy that is wirehaired. To find out most quickly whether he carries the allele for smooth hair, he should be mated to what type of female? How
will you know based on the mating?