1. In squash the gene, W for white color, is
dominant over its allele, w for yellow color. What is the expected F1
from a cross between heterozygous white and yellow
In Rabbit brown fur (B) is dominant to white fur (b). A brown
furred Rabbit named Charley is crossed with a white furred Rabbit and the progeny occur in the ratio of 50% brown to
50% white. What is the likely genotype of Charley ?
3. The ability to
roll one's tongue into a U-shape is determined by the presence
of a non-sex linked dominant gene, T. A man, unable to roll
his tongue, and a woman able to roll hers, have four
children. The woman's mother couldn't roll her tongue, but her father
could. Of their four children how many might you expect to
unable to roll their tongues ?
4. A couple has
four children whose blood types are A, B, and AB. Which of the parental
genotypes is capable of producing the blood types of
this couples children ?
5. A human recessive genetic disease, termed Charlyitis,
is found on chromosome 12 and is often fatal. Suppose by chance
that a boy, Michael, who has this disease lives past puberty and
marries a normal woman, but whose father also had Charlyitis.
If this couple have any children what is the probability that the
children will have Charlyitis ?
6. An allele for brown eyes B is dominant over
that for blue eyes b. A couple of whom one is brown-eyed and
the other blue-eyed have
eight children, all brown eyed. What would be the
genetic make up of each parent in this regard? For each parent state whether
they are homozygous or heterozygous.
A blue-eyed man, both of whose parents were brown-eyed, marries a woman. They
have one child who is blue-eyed. What are the genotypes of all the individuals
8. A brown-eyed man whose father was
brown-eyed and whose mother was blue-eyed married a blue-eyed woman whose
father and mother were both brown-eyed. The couple has a blue-eyed son.
For which of the individuals mentioned can you be sure of the genotype? What
are the genotypes? What genotypes are possible for the others?
9. A hybrid pink snapdragon was crossed with a pure white
one. Red flower colour is incompletely dominant. Make
a diagram to show:the gene constitution
of the parents
genotypic and phenotypic ratios of the F2 generation]
the garden pea, Mendel found that yellow seed colour
was dominant to green and round seed shape was dominant to shrunken. Determine
the phenotypic and genotypic ratios for the F1 generation and the phenotypic
ratio for the F2 if a plant with homozygous rounded yellow seeds is crossed
with a plant with shrunken green seeds.
Tall tomato plants are produced by the action of a dominant allele T and
dwarf plants by its recessive allele t. Hairy stems are produced by a dominant
gene H and hairless stems by its recessive allele h. A dihybrid
tall, hairy plant is crossed with a dwarf hairless tomato plant. Determine the
phenotypic ratio for the F1 generation.
12 Black coat
colour in Cocker Spaniels is dominant, while red coat
colour is recessive; solid pattern is dominant, while
spotted pattern is recessive. A solid black male is mated to a solid red female
and produces a litter of six pups: two solid black, two solid red, one black
and white, and one red and white. Determine the genotypes of the parents.
fissure is controlled by a dominant allele and a smooth chin by a recessive
allele. If the parents were heterozygous for the trait, the
chance of producing a child with a chin fissure?
14. Albinism (lack of skin
pigmentation) is caused by a recessive autosomal
allele. A man and a woman, both normally pigmented, have an albino child. The
mother is now pregnant again, and her doctor tells her she is carrying fraternal
twins (resulting from two eggs between fertilized by separate sperm). What is
the probability that both twins will have normal pigmentation?
15. In snapdragons plant color
shows an incomplete dominance. Heterozygous plants have pink flowers, where as
the two homozygotes have red flowers or white
flowers. Two pink flowers are crossed. What proportion of their progeny would
you predict would be pink?
16 If two heterozygous parents,
CcDd, were crossed how many possible combinations of GENOTYPES in
17. If tall is
dominant to short, and purple flowers are dominant to white flowers, what is
the phenotypic ratio of the potential offspring if you cross a short, white
flower with a homozygous dominant tall, heterozygous purple flower?
18. Black fur in mice is
dominant to brown fur (B – dominant allele, b-recessive allele). Short tails
are dominant to long tails (T – dominant allele,
t-recessive allele). What fraction of the progeny of the cross BbTt X BBtt would you predict
would have black fur and long tails?
19. You are a genetic counselor and you have a couple that
comes to you for advice. The mother is heterozygous for normal and sickle
cell hemoglobin (HbA/HbS) and
heterozygous for types A and B glucose-6-phosphate dehydrogenase
(G6PDA/G6PDB) and the father is
heterozygous for sickle cell hemoglobin and hemoglobin C (HbC/HbS)
and hemizygous for glucose-6-phosphate dehydrogenase type A- (G6PDA-).
genotypes and phenotypes do you predict for their offspring?
frequencies of the different combinations (both genotypes and phenotypes) are
c. What Mendelian principle or principles are illustrated by this
a. What would the genotype frequencies
and allele frequencies be in the next generation?
b. What is your long term prediction
for allele frequencies if selection remains the same?
- A rooster with gray feathers is mated with a hen of the
same phenotype. Among their offspring, 15 chicks are gray, 6 are black,
and 8 are white. What is the simplest explanation for the inheritance of
these colors in chickens? What offspring would you predict from the mating
of a gray rooster and a black hen?
- In some plants, a true-breeding, red-flowered strain gives
all pink flowers when crossed with a white-flowered strain: RR
(red) x rr
(white) --- Rr (pink). If flower position
(axial or terminal) is inherited as it is in peas (i.e., axial is dominant
to terminal), what will be the ratios of genotypes and phenotypes of the
generation resulting from the following cross: axial-red (true-breeding) x
terminal-white? What will be the ratios in the F2
- Flower position, stem length, and seed shape were three
characters that Mendel studied. Each is controlled by an independently
assorting gene and has dominant and recessive expression as follows:
- If a plant that is heterozygous for any two characters
were allowed to self-fertilize, what proportion of the offspring would be
expected to be as follows? (Note: Use the rules of probability
instead of a huge Punnett square.)
- homozygous for the three dominant
- homozygous for the three recessive
- homozygous for axial and tall,
heterozygous for seed shape
- A black guinea pig crossed with an albino guinea pig
produced 12 black offspring. When the albino was crossed with a second
black one, 7 blacks and 5 albinos were obtained. What is the best
explanation for this genetic situation? Write genotypes for the parents,
gametes, and offspring.
- In sesame plants, the one-pod condition (P) is
dominant to the three-pod condition (p), and normal leaf (L)
is dominant to wrinkled leaf (l). Pod type and leaf type are
inherited independently. Determine the genotypes for the two parents for
all possible matings producing the following
- 318 one-pod normal, 98 one-pod
- 323 three-pod normal, 106 three-pod
- 401 one-pod normal
- 150 one-pod normal, 147 one-pod
wrinkled, 51 three-pod normal, 48 three-pod wrinkled
- 223 one-pod normal, 72 one-pod
wrinkled, 76 three-pod normal, 27 three-pod wrinkled
- Color patterns in a species of duck is determined by one gene with three
alleles. Alleles H and I are semidominant
(i.e., incomplete dominance), and allele i
is recessive to both. How many phenotypes are possible in a flock of ducks
that contains all the possible combinations of these three alleles.
- Phenylketonuria (PKU) is an inherited disease caused
by a recessive allele. If a woman and her husband are both carriers, what
is the probability of each of the following?
- all three of their children will be
of normal phenotype
- one or more of the three
children will have the disease
- all three children will have the
- at leastone child will be phenotypically
- The genotype of F1 individuals in a dihybrid cross is AaBb.
Assuming independent assortment of these four genes, what are the
probabilities that F2 offspring would have the following
- A stray black cat with unusual rounded, curled black ears
was adopted by a family in California.
Hundreds of descendants of the cat have since been born, and cat fanciers
hope to develop the "curl" cat into a show breed. Suppose you owned
the first curl cat and wanted to develop a true-breeding variety. How
would you determine whether the curl allele is dominant or recessive? How
would you select for true-breeding cats? How would you know they are true
- What is the probability that each of the following pairs
of parents will produce the indicated offspring (assume independent
assortment of all gene pairs)?
- AABB x aabb---
- AABb x AaBb ---
- AaBb x AaBb ---
- aaBb x AABb--- AaBb
- In tigers, a recessive allele causes an absence of fur
pigmentation (a "white tiger") and a cross-eyed condition. If
two phenotypically normal tigers that are
heterozygous at this locus were mated, what percentage of their offspring
will be cross-eyed? What percentage will be white?
- In corn plants, a dominant allele I inhibits kernel color, while the recessive allele i permits color when homozygous. At a different
locus, the dominant gene P causes purple kernel color, while the
homozygous recessive genotype pp causes red kernels. If plants
heterozygous at both loci are crossed, what will be the phenotypic ratio
of the F1 generation?
- A man has six fingers on each hand and six toes on each
foot. His wife and their daughter have the normal number of digits. Extra digits is a dominant trait. What fraction of this
couple's children would be expected to have extra digits?
- In mice, black color (B) is dominant to white (b).
At a different locus, a dominant allele (A) produces a band of
yellow just below the tip of each hair in mice with black fur. This gives
a frosted appearance known as agouti. Expression of the recessive allele (a)
results in a solid coat color. If mice that are heterozygous at both loci
are crossed, what will be the expected phenotypic ratio of their
- If the litter resulting from the mating of two
short-tailed cats contains three kittens without tails, two with long
tails, and six with short tails, what would be the simplest way of
explaining the inheritance of tail length in these cats? Show genotypes
(i.e., of all of the individuals mentioned).
- In watermelons the genes for green color and for short
shape are dominant over their alleles for striped color and for long
shape. Suppose a plant with long striped fruit is crossed with a plant
heterozygous for both these characters. What phenotypes would this cross
produce and in what ratios?
- In guinea pigs, black fur (B) is dominant over
white fur (b). If one half of a particular litter were white, the
genetic makeup of the parents was what?
- In sorghum plants, red stem is dominant over green stem.
If 1,000 seeds from a sorghum plant germinated to produce 760 red plants
and 240 green plants, it would be most reasonable to assume that the
parental genotypes were what
- B is a dominant allele coding for
black fur on rabbits and b is a recessive allele coding for white fur on
rabbits. Fill in the following blanks with the correct cross of the
- A man and a woman each have dark eyes, dark hair, and
freckles. The genes for these traits assort independently. The woman is
heterozygous for each of these traits, but the man is homozygous. The
dominance relationships of the alleles are as follows:
- What is the probability that their
child will share the parents' phenotype?
- What is the probability that the child
will share the same genotype as the mother?
- As the father?
- In cats with the Manx trait, the M (dominant)
allele causes a short or absent tail, whereas the m allele confers a
normal, long tail. Cats of genotype MM die as embryos. If two Manx
cats mate, what is the probability that each living kitten has a long
- Domesticated hens with white feathers and large, single
combs mate with roosters that have dark feathers and small combs. The
offspring all resemble their mothers for these two traits. (a) Which
alleles are dominant, and which are recessive? (b) If the F1 generation are crossed with each other, what fraction
of the F2 generation would be expected to have dark feathers and large,
- If the dominant allele K is necessary for hearing, and the
dominant allele M of another independent loci (i.e., not linked)
results in deafness no matter what other genes are present, what
percentage of the offspring produced by the cross kkMm
x Kkmm will be deaf?
- Work out the genotype of
all carriers and affected individuals.