Download genetics practice problems

GENETICS PRACTICE PROBLEMS
1.
2.
3.
4.
5.
A brown mink, when crossed with a
silver-blue mink produced all brown
offspring. When these F1 mink were
crossed among themselves they
produced 47 brown animals and 15 silverblue animals (F2 generation). Determine
all the genotypes and phenotypes, and
their relative ratios, in the F1 and F2
generations
A brown mouse is mated with two female
black mice. When each female has
produced several litters of young, the first
female has had 48 black and the second
female has had 14 black and 11 brown
young. Determine the pattern of
inheritance of coat colour and the
genotypes of all the parents
In turkeys, a dominant gene R produces
the familiar bronze colour; its recessive
allele r results in red. Another dominant
gene H results in normal feathers; its
recessive allele h produces feathers
without webbing, so that they resemble
tufts of hair. Two bronze turkeys with
normal feathers were mated, and their
offspring consisted of 9 bronze with
normal feathers, 3 bronze with hairy
feathers, 3 red with normal feathers, and
1 red with hairy feathers. What were the
genotypes of the parents?
In horses, black is dependent upon a
dominant gene, B, and chestnut upon its
recessive allele, b. The trotting gait is
due to a dominant allele T, and the pacing
gait to its recessive allele, t. If a
homozygous black pacer is mated to a
homozygous chestnut trotter, what will be
the appearance of the F1 generation?
Yellow guinea pigs crossed with white
ones always produce cream coloured
offspring. Two cream coloured guinea
pigs when crossed produced yellow,
cream and white offspring in the ratio of 1
yellow:2 cream: 1 white. How are these
colours inherited?
6.
In humans, the blood groups are
produced by various combinations of
three alleles IA, IB , and IO. Blood types A
and B are codominant and both and both
A and B are dominant over O. Suppose a
child is of blood type A and the mother is
of type O. What type or types may the
father belong to?
7.
A mother and father with normal colour
vision produce six male children, two of
whom exhibit red-green colourblindness.
Their five female children exhibit normal
colour vision. Ignoring the fact that these
parents ought to seek some family
planning advice, explain the inheritance
of red-green colourblindness in their male
children.
8.
9.
A cross between a black cat and a tan cat
produces a tabby pattern (black & tan fur
together).
a) What pattern of inheritance does
this illustrate?
b) What percent of kittens would
have tan fur if a tabby cat is
crossed with a black cat?
In squash, a gene for white colour (W) is
dominant over its allele for yellow colour
(w). Give the genotypic and phenotypic
ratios for the results of each of the
following crosses:
a) WW x ww
b) Ww x ww
c) Ww x Ww
10. If pollen from anthers of a heterozygous
white-fruited squash plant is placed on
the pistil of a yellow-fruited plant show,
using ratios, the genotypes and
phenotypes you would expect the seeds
from this cross to produce.
11. In human beings, brown eyes are usually
dominant over blue eyes. Suppose a
blue-eyed man marries a brown-eyed
woman whose father was blue-eyed.
What proportion of their children would
you predict will have blue eyes?
12. A brown-eyed man whose father was
brown-eyed and whose mother was blueeyed 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 genotypes? What are
their genotypes? What genotypes are
possible for the others?
13. 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.
14. When Mexican Hairless dogs are crossed
with normal-haired dogs, about half of the
pups are hairless and half have hair.
When, however, two Mexican Hairless
dogs are mated, about a third of the pups
produced have hair, about two thirds are
hairless, and some deformed puppies are
born dead. Explain these results. Show
genotypes.
Monohybrid Cross
1.
A purple-flowered pea plant is crossed
with a white-flowered pea plant. All the F1
plants produce purple flowers. When the
F1 plants are crossed with each other, 401
of the F2 plants have purple flowers and
131 have white flowers. What are the
genotypes of the parental and F1
generation plants?
2.
In tomatoes, red fruit colour is dominant
to yellow. Suppose a tomato plant
homozygous for red is crossed with one
homozygous for yellow. Determine the
appearance of
a)
(a) the F1
(b) the F2
(c) the offspring of a cross of the F1
back to the original red parent
(d) the offspring of a cross of the F1
back to the yellow parent
d)
3.
A red-fruited tomato plant, when crossed
with a yellow-fruited one, produces
progeny about half of which are redfruited and half are yellow-fruited. What
are the genotypes of the parents?
4.
In guinea pigs, rough coat (R) is dominant
over smooth coat (r). A rough-coated
guinea pig is bred to a smooth one,
giving 8 rough and 7 smooth progeny in
the F1.
a)
b)
5.
What are the genotypes of the
parents and their offspring?
If one of the F1 animals is mated to its
rough parent, what progeny would
you expect?
c)
e)
Dihybrid Cross
1.
In rabbits, C=agouti coat colour,
cch=chinchilla, ch=Himalayan, and
c=albino. The four alleles constitute a
multiple allelic series. The agouti is
dominant to the other three alleles and
albino  c is recessive to the other three
alleles. Chinchilla is dominant to
Himalayan. Determine the phenotypes of
progeny from the following crosses.
a)
b)
c)
d)
e)
f)
CC X cc
Ccch X Cc
Cc X Cc
Cch X chc
Cch X cc
Cchch X chc
In Jimsonweed purple flower (P) is
dominant to white (p), and spiny pods (S)
are dominant to smooth (s). In a cross
between a Jimsonweed homozygous for
white flowers and spiny pods and one
homozygous for Purple flowers and
Smooth pods, determine the following:
a)
b)
c)
d)
2.
Purple flowers are dominant to white
flowers in the Jimsonweed. When a
particular purple-flowered Jimsonweed is
self-pollinated, there are 28 purpleflowered and 10 white flowered progeny.
What proportion of the purple-flowered
progeny are true-breeding?
Multiple Alleles
1.
b)
an O child from the marriage of two A
individuals
an A child from the marriage of an A
to a B
an AB child from the marriage of an A
to an O
an O child from the marriage of an AB
to an A
an A child from the marriage of an AB
to a B
What phenotypes would you expect to
find in progeny from the following
Jimsonweed crosses?
a)
b)
c)
d)
e)
f)
3.
the phenotype of the F1
the phenotype of the F2
the progeny of a cross of the F1 back
to the white, spiny parent
the progeny of a cross of the F1 back
to the purple, smooth parent
PPss
PpSS
PpSs
PpSs
PpSs
PpSs
X
X
X
X
X
X
ppSS
ppss
PpSS
PpSs
Ppss
ppss
In summer squash white fruit (W) is
dominant over yellow (w), and diskshaped fruit (D) is dominant over sphereshaped fruit (d). In the following
problems, the phenotypes of the parents
and their offspring are given. Determine
the genotypes of the parents in each
case.
a)
Parents
White, disk X Yellow, sphere
b)
White, sphere X White sphere
c)
Yellow disk X White sphere
d)
White disk X Yellow sphere
Offspring
½ White disk and ½ white sphere
Codominant Alleles
1.
In humans the three alleles IA, IB, and I
constitutes a multiple allelic series that
determine the ABO blood group system.
For the following problems state whether
the child mentioned can actually be
produced from the marriage. EXPLAIN
YOUR ANSWER.
¾ White sphere and ¼ yellow
sphere
all white disk
¼ White disk, ¼ White sphere,
¼ Yellow disk, ¼ Yellow sphere