SBI 3U
Genetics Problem Sets
Name: ________________
This set of genetics problems will be used for the next few days in class. Make sure you have it
with you every day!!
Set 1. Monohybrid Cross (p. 189)
1.
Give the possible genotypes of the offspring from the following crosses:
AA x aa; Bb x bb; CC x Cc; Dd x Dd; ee x ee
2.
In a certain animal, black fur (B) is dominant to white fur (b). Determine the expected genotypic and
phenotypic ratios resulting from crosses between:
a) homozygous black x white
b) two heterozygous blacks
c) heterozygous black x white
3.
In cattle, hornless is dominant over horned.
a) If two cattle are mated, one pure horned and one pure hornless, what will be the phenotype and
genotype of the offspring.
b) If two of these offspring were mated, what would be the appearance of their offspring?
Set 2. Dihybrid Cross (p. 211-212)
4.
In the fruit fly, vestigial wings (small and useless) and ebony (black) body colour are produced by two
recessive genes located on different chromosomes. The normal alleles, long wings and grey body colour,
are dominant. What offspring would be expected if a vestigial-winged ebony male is crossed with a
homozygous normal female? If the F1 from this cross were permitted to mate randomly among themselves,
what offspring would be expected in the F2?
5.
A black pacer horse was crossed with a chestnut trotter and all the F 1 offspring were black trotters. Show
this cross and find the expected ratios of genotypes and of phenotypes in the F 2 generation.
6.
Assume that curly hair (C) is dominant to straight hair (c). Albinism is a condition in which cells that
normally produce pigment, do not do so. The allele for skin albinism (n) is recessive to the normal allele
(N). A woman with curly hair and albinism and a man with straight hair and normal skin pigment have a
child who has straight hair and is an albino. Completely show this cross.
Set 3. Incomplete Dominance (p. 194)
7.
A gene that controls feather structure in chickens causes extremely disrupted feathers (known as frizzled)
when homozygous (HFHF) and mild frizzle when heterozygous (HFHN) and normal when homozygous
(HNHN). Show the results, in the F1 and F2 generations, when normal and extremely frizzled chickens are
crossed.
8.
In snapdragon plants, tall is dominant to short and red flowers are incompletely dominant to white flowers
resulting in pink hybrids. Two pink-flowered plants are interbred, one being homozygous for tall and the
other being short.
a) Find the expected ratio of F1 phenotypes from the above cross and explain the genotype of parents
and offspring.
b) Which offspring from the above cross should be mated in order to produce offspring all of which have
pink flowers? Show this cross and describe the resulting phenotypes.
Set 4. Co-dominance (p. 195)
9.
Coat colour in shorthorn cattle is an example of co-dominance. The two homozygous genotypes produce
red and white coats while the heterozygous genotypes produce a roan coat (a mixture of red and white
hairs). Show the results in the F1 and F2 generations when a white and a red shorthorn are crossed.
Set 5. Multiple Alleles (p. 195)
10.
A wealthy, elderly couple die together in an accident. Soon, a man shows up to claim their fortune,
contending that he is their only son who ran away from home when he was a boy. Other relatives dispute
this claim. Hospital records show that the deceased couple were blood types AB and O. Can they tell if
the claimant was an imposture using blood typing? Explain your answer using punnet squares.
11.
Suppose two newborn babies were accidentally mixed up in the hospital. In an effort to determine to which
parents each baby belonged, the blood type of the babies and the parents were determined to be as
follows:
Baby 1: Type O
Baby 2: Type A
Mrs. Brown: Type B
Mr. Brown: Type AB
Mrs. Smith: Type B
Mr. Smith: Type B
Determine which baby belongs to which parents and the genotype of each person.
Set 6. Sex-Linked (p. 200)
12.
In humans, there is a gene on the X chromosome, which controls the formation of the colour-sensitive cells
in the retina of the eye. These cells are necessary for the distinction of red and green. The recessive form
of this gene results in red-green colour-blindness. Give the phenotypes and genotypes of possible
offspring from the following couples:
a) colour-blind man x normal woman
b) colour-blind woman x normal man
c) female carrier x normal man
13.
A woman has a brother with hemophilia; both of her parents are normal. This is a sex-linked recessive
gene. She wishes to marry a man with no history of hemophilia in his family. What are the chances of their
children having the disease?
14.
In cats there is a gene for coat colour, which is intermediate; the hybrid shows incomplete dominance. The
trait is also sex-linked. There is one gene for yellow and another version for black, but a heterozygous cat
has a peculiar mixture of yellow and black called tortoise shell. What type of kittens would result from the
following crosses:
a) a black female and yellow male
b) tortoise shell female and black male
Tortoise shell males are rare and usually sterile. Explain.
Set 7. Pedigrees (p. 197-199)
15.
Determine the genotype, where possible, of each individual in the following pedigree for albinism. Use the
letter “a” to represent the gene for albinism.
I
II
III
IV
“ODD” Genetics Problems
SBI 3U
1.
When a red flowered four-o-clock plant is crossed with a white flowered four-o-clock
plant, all the offspring have pink flowers. The F1 pink flowered plants are crossed to
obtain an F2 generation.
a)
b)
c)
2.
By means of Punnett squares, show the above crosses. State the phenotypes
and genotypes of each generation. Include the phenotypic ratio for the F2
generation.
What offspring could result from a cross between a pink and a red flowered plant?
Is it possible to get pink flowered plants which are pure breeding for pink flowers?
Explain.
Three newborn babies had their identification bracelets accidentally mixed up. The blood
types of the babies and parents were as follows:
Baby X
Baby Y
Baby Z
Type A
Type O
Type AB
Mr. Brown
Mr. Black
Mr. White
Type AB
Type O
Type A
Mrs. Brown Type O
Mrs. Black Type O
Mrs. White Type B
Show which baby belongs to which parents and indicate how you determined this.
3.
Colour blindness is a recessive X-linked trait.
A female with normal vision, whose father was colour blind, marries a normal visioned
man. What are the chances of them having:
a) a colour blind daughter
b) a colour blind son
c) If a male is colour blind, from which parent did he inherit this trait? Explain.
4.
A man and a woman, both of normal vision have:
(1) a colour blind son who has a daughter of normal vision,
(2) a daughter of normal vision who has one colour blind and one normal son, and
(3) another daughter of normal vision who has five sons, all normal visioned.
What are the probable genotypes of grandparents, children and grandchildren?
5.
The absence of legs in cattle (“amputated”) has been attributed to a recessive lethal
gene. A normal bull is mated with a normal cow and they produce an amputated calf
(usually dead at birth). The same parents are mated again:
a) What is the chance of the next calf being amputated?
b) What is the chance of them having two amputated calves?
6.
When chickens with splashed white feathers are crossed with black feathered birds, their
offspring are all slate blue (Blue Andalusian). When Blue Andalusian are crossed among
themselves, they produce white, blue and black offspring in the ratio 1:2:1 respectively.
a) How are these feather types inherited?
b) Using appropriate symbols, indicate the genotypes for each phenotype.
7.
In the Mexican Hairless breed of dogs, the hairless condition is produced by the
heterozygous genotype. Normal dogs are homozygous recessive. Puppies homozygous
for the dominant gene are usually born dead with abnormalities of the mouth and
absence of external ears. What would be the expected phenotypes and genotypes of a
cross between two hairless dogs? Show all work.
8.
A dominant allele ‘L’ governs short hair in guinea pigs and its recessive allele ‘l’ governs
long hair. Codominant alleles at an independently assorting locus specify hair colour,
such that CYCY = yellow, CYCW = cream (yellow and white hairs present) and CWCW =
white. Predict the phenotype ratio from matings between heterozygous short cream pigs.
9.
In cats, black coat (B) and ginger coat (G) are incompletely dominant. Both genes occur
on the X chromosome. When B and G are present together, a tortoise shell coat results.
A black female cat is crossed with a ginger male.
a) What types of offspring might be produced in the F1 and F2 generations? Describe
their sex and coat colour.
b) Is it possible to get a male with a tortoise shell coat? Explain.
c) Is it possible to get a ginger female cat? Explain.
10.
Baldness is a sex-influenced trait.
a) What are the possible results of a mating between a normal male and a heterozygous
normal woman. Give the phenotypes and sex of children.
b) Cross a homozygous bald man with a heterozygous woman and indicate the results.