Academy Biology Genetics Problems
On a separate sheet of paper solve
each of these problems. Show all work for complete credit, including Punnett
squares and complete sentence answers where required.
In humans, the gene for dark
colored eyes (black or brown) is dominant over the genes for light colored eyes
(blue, green, or gray). A man with brown eyes marries a woman with blue eyes.
They have two children, a boy with brown eyes and a girl with blue eyes. What
are the genotypes all of the members of the family?
A man with brown eyes marries a
woman with blue eyes. They have a family of six brown eyed children – four
girls and two boys. What are the most likely genotypes and phenotypes of all of
the members of this family?
A brown eyed man marries a blue
eyed woman. They have five children, two with brown eyes and three with blue
eyes. What are the most genotypes of all of the members of this family?
A brown eyed man with a blue
eyed mother marries a brown eyed woman with a blue eyed father. What is the
probability that their first child will be blue eyed? That the second child
will be blue eyed? That the third child will be a blue eyed boy?
In morning glories, the heterozygous phenotype
for red flowers, R, and white flowers, r is pink flowers. A plant with pink
blossoms is isolated from the others and allowed to self pollinate. Predict the
genotypic and phenotypic ratio which would be expected to result from this
In the cross above, the plant
was allowed to self pollinate. Why then is this considered a form of sexual
reproduction when there is apparently only one parent?
In the morning glories,
described above, a line of plants breeds true for red blossoms. Predict the
results expected if a garden were planted from seeds derived from a cross
between one of the red flowerd plants with a pink flowered plant.
In humans, the inheritance of
blood type (A, B, or O) is determined by at least three alleles. The allele A
codes for type A blood. The allele B codes for type B blood. Neither allele A
or B is dominant over the other, the heterozygous condition resulting in blood
type AB. Both alleles A, and B are however dominant over blood type O. A man and his wife both have type A blood. Their
child is born with blood type O. How is this explained?
A man whose father is type B
and whose mother is type A, has blood type A. He marries a type A woman, whose
parents had the same blood types as his parents. What are the genotypes of the
man and his wife and what is the probability that their first child will
inherit type A blood?
A type A man whose mother was
type O marries a woman with type B blood. Their son has type B blood. This son
marries a girl with type B blood. They have six children. Five are type B and
one is type O. What are the genotypes of the man, woman, son, girl, and
In Andalusian fowl, the plumage
for black feathers and the plumage for white feathers are codominant, the
heterozygous condition resulting in mottled (black + white) plumage. A mottled
hen is bred with a white rooster. Predict the genotypic and phenotypic ratio of
the offspring. Explain why the mottled condition is considered codominant
rather than incomplete dominance.
In corn, the gene for purple
kernels, P, is dominant to the gene for yellow kernels, p. The gene for
starchy, S, is dominant to sweet kernels, s. (Starchy ones appear full while
sweet ones appear wrinkled). The two traits are known to be inherited
independently. A strain of corn breeds
true for purple, sweet kernels. Another strain breeds true for yellow, starchy
kernels. What are the genotypes for both strains of corn plants? Assume the
plants were cross bred. Predict the outcome of this cross on the next
generation of corn plants?
The corn plants from the first generation, above (F1), are now allowed
to self pollinate. What is the expected genotypic and phenotypic ratio expected
in the F2 generation of corn plants?
The F1 generation of plants
above are backcrossed with the parent which is recessive for both traits.
Predict the expected genotypic and phenotypic ratio for this cross.
Determine the genotypes for the
two parent corn plants for each of the following results:
318 purple starchy kernels, 98
purple sweet kernels
323 purple starchy, 106 yellow
410 purple starchy
150 purple starchy, 147 yellow
sweet, 142 yellow starchy, 151 purple sweet
223 purple starchy, 72 purple
sweet, 76 yellow starchy, 27 yellow sweet.
In Drosphila, at least two
genes are involved in eye color, S and B. The genes are inherited independently
of one another. If both dominant genes are inherited (at least one S and one B)
the wild type eye color (red) results. If the homozygous recessive ss is
inherited the eyes are scarlet red in color but if the other homozygous
recessive gene is inheritied, bb, brown eye color results. The double
homozygous recessive condition, ssbb, results in white eyed flies which often
die as juveniles. A strain of flies with
scarlet red eyes are bred with another strain with brown eyes. Predict the
expected genotypic and phenotypic ratio of this cross.